# Help designing a repetitive dado jig



## jevansoh (Nov 12, 2014)

Hi,

This is my first post and I'm not only a newbie here at routerforums but I'm also a total newbie to woodworking to the point that I haven't even purchased a router or table saw yet.

I have a very specific need for a project that will require making hundreds of evenly spaced dadoes/grooves and really need help figuring out the easiest way of doing it.

I'm making roughly 2' x 4' acoustical diffusers that will need to have a groove/dado that is only 3/16" wide (for undersized 1/4" plywood), 3/8" deep, and spaced exactly 1.5" apart.

I will be making at least 20 of these, and each one will have 12 grooves spaced 1.5" apart, only 3/16" wide and 3/8" deep.

I was originally going to buy a table saw and dado set but I cannot find a dado set that will allow me to cut under 1/4" wide dadoes. 

I then thought about buying a thin kerf blade and regular kerf blade and just stacking them to make my own cheap dado set but I'm having a lot of trouble finding two blades that equal exactly 3/16" to fit my 1/4" nominal plywood.

To help visualize what I'm making (since I cannot post links yet) just think of slatwall panels only instead of t-shaped grooves they will just be flat/straight grooves and instead of the slats being 2.5"-3" wide, they will only be 1.5" wide.

I've looked at several home made exact width dado jigs for a router, but it would take forever (and probably wouldn't be very accurate and I do need accuracy for this project) to measure and line up 12 grooves per board and then do it 20 times or more... That's a minimum of 240 measurements, unclamping, clamping, etc.

I want to make a jig that will allow me to cut perfect 3/16" wide, 3/8" deep dadoes/grooves spaced 1.5" apart and make it as easily as possibly and fool proof as possible since I have no experience.

If only 1/4" plywood were really 1/4" I could use a dado blade and table saw and have no issues, but alas, I really need some ideas. 

The only good news is that I don't need it to be adjustable because I'll always be using the same plywood and I'll always be making 3/16" grooves, 3/8" deep, every 1.5" apart. The bad news is I have no idea what the best tool to use is or how to design this for a finished product that will be roughly 2ft x 4ft with 12 of these grooves per board.

Thank you so much in advance for your ideas, help and support. I've spent about 30 hours in the last week researching this forum, YouTube videos, and Google, and have come up with many ideas, but none of which I really know how to engineer and build properly. I finally landed here, made an account, and hope to become a master at this and one day look back on this, my first post here, and chuckle at how inexperienced I "was" and see how far I've come.

--Jason


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## Cherryville Chuck (Sep 28, 2010)

Welcome to the forum Jason. Check out the jig that Otis (OPG3) posted in an old thread. It may give you some ideas. http://www.routerforums.com/general-routing/40389-totally-disgusted-2.html

A dado can be set to give the right width groove for uou. You would use one side plate and the 1/16 plate that comes with them and then use some dado shims (Lee Valley sells them for one) to fine tune the fit.

If you use the router bit 3/8" deep is considered too heavy a cut for a single pass in a 3/16" bit. The general rule is only as deep as the diameter per pass.


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## Gaffboat (Mar 11, 2012)

I think the easiest way would be to cut them on a table saw. Most table saw blades have a 1/8" kerf. I would make a 1/16" removable shim that runs the length of the fence and then:

1. Set the fence for the first cut with the shim in place and cut all the pieces. 
2. Remove the shim and recut all the pieces (giving you your 3/16").
3. Move the fence to the next position. Put the shim back in place and rinse and repeat steps 1 and 2 until finished.

Whatever method you use will take time but this way you only have to make one set-up for each cut.


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## CharleyL (Feb 28, 2009)

You can stack saw blades if they both have the same number of teeth and are the same diameter. A dado blade assembled from one side blade and the 1/16 chipper with shims to get the spacing exact to fit your plywood would be the best way to cut accurate dados quickly on a table saw. If you cut some strips that are exactly 1 1/2 inches wide you can use them between the fence and the work, removing one strip for each pass. I would cut a dado in all of the boards, then remove one spacer and cut them all again, then remove another spacer, etc until all of the Dados have been cut. Tape or clamp the spacers in place to keep them from moving while making the cuts. This is an accurate way of getting the incremental spacing needed between the cuts. You don't move the fence at all. I hope I'm clear with this. If not, let me know and I'll try to describe it again.

Charley


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## MT Stringer (Aug 15, 2012)

I used a pair of cheep 7 1/4 inch circular saw rip blades and a small shim or two to get the desired width. One pass on the table saw for each dado.

Might take a little thinking to come up with a spacing jig.


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## greenacres2 (Dec 23, 2011)

Sounds like the perfect job for an Incra LS system on a router table, using a 3/16" bit. Once you locate the center of the stock on the Incra system you could even change the bit size so that if you get a batch of 7/32" stock, you still get the same spacing between grooves.

Shoot, with a large enough table, the 32" Incra could handle doing the grooves in the 24" length across the 48" width. (the 25" could do the job in theory, but i'd not want to get that close to the limit of travel with accuracy being that important) Simply start in the middle and work toward the edges with each adjustment of the positioner. Easily repeatable system too.

earl

edit--if you did buy a table saw, and use Mike's suggestion of 7 1/4" blades--the LS positioner works on a table saw also.


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## DaninVan (Jan 1, 2012)

Hey, Jason; welcome!
You didn't mention what your 2' x 4' panels are made of? MDF or plywood?
If they're MDF you are going to be making a LOT of very nasty dust... please don't underestimate how bad this stuff is for your lungs. Plywood's not much better.
An alternate system could be alternating the vertical 'fins' with 1.5" wide full length spacers, butted up tight to the fin and glued to the base panel. Tight fit and no dadoing required. make everything from the same 1/4" plywood.


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## boogalee (Nov 24, 2010)

Is this what you are trying to build.

If so:
1. Do you plan on buying a router?
or
2. Do you plan on buying a table saw?

In your profile I don't see any tools you have listed (such as a circular saw).


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## jw2170 (Jan 24, 2008)

Rockler Router Fluting Jig - Power Router Accessories - Amazon.com


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## old55 (Aug 11, 2013)

Welcome to the forum Jason


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## PhilBa (Sep 25, 2014)

I'm surprised no one has mentioned "undersized" plywood router bits. They are designed to cut dados for modern plywood that is slightly thinner than the stated width. Rockler has 'em but other outfits do as well. From the sound of it, that's exactly what you were asking for.


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## Stick486 (Jan 4, 2013)

jevansoh said:


> Hi,
> 
> I have a very specific need for a project that will require making hundreds of evenly spaced dadoes/grooves and really need help figuring out the easiest way of doing it.
> 
> ...


something the size of a Bosch Colt in a plunge base would be made to order for this...
Bosch PR20EVSPK Colt Palm Grip 5.6 Amp 1 HP Variable-Speed Combination Plunge and Fixed-Base Router Kit

your bit...
Freud Tools
Freud Tools | 7/32" (Dia.) Mortising Bit

FWIW... 3/8" is a might deep.. suggest you go for a 1/4"... or less


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## jevansoh (Nov 12, 2014)

Cherryville Chuck said:


> Welcome to the forum Jason. Check out the jig that Otis (OPG3) posted in an old thread. It may give you some ideas.
> 
> A dado can be set to give the right width groove for you. You would use one side plate and the 1/16 plate that comes with them and then use some dado shims (Lee Valley sells them for one) to fine tune the fit.
> 
> If you use the router bit 3/8" deep is considered too heavy a cut for a single pass in a 3/16" bit. The general rule is only as deep as the diameter per pass.


Thanks for the info and suggestion.

I'm obviously a total newbie, but I've read all the wonderful tips and suggestions made in this thread up to this point and have spent some time researching the different jigs suggested.

Since I have so many panels to make and since they are so large, I keep coming back to wanting to use a dado set for a table saw.

I thought in order to use a dado set (please correct me if I'm wrong, as it seems I probably am if I'm understanding your suggestion correctly) you had to use two outside blades (which are normally 1/8" thick each) plus whatever chipper(s) and shim(s) between them, like a sandwich.

Are you saying I could use just one 1/8" blade and a 1/6" chipper, and nothing more, to get a 3/16" dado? If so, I believe this, along with some spacers suggested in another post will probably be the easiest and fastest (and cheapest as I will only need a table saw instead of both a table saw for my ripping and a router for my dadoes) method to cut my grooves/dadoes.

I've been researching 1/4" stock and am finding that actual widths aren't 3/16ths after all, and in fact they range from .201" to .230" roughly, so I suppose I'd need some shims, too.

Instead of purchasing a whole dado set, is it possible to just purchase a 1/16" chipper and some shims and then just use a regular 1/8" kerf blade?

I've also thought about purchasing the Vermont American Wobble Dado set because it's cheap and the only one I've seen that allows dadoes below 1/4". I've read they have a bad reputation, but it seems that comes mainly from wide dadoes. Do you think it would be a good way to start, or should I stick with trying to find a regular stacked dado set that will work for my narrow grooves?

Based on my reply, do you think I understand your suggestion correctly and do you think this would be the best way to go?

Thanks again for all your help!

--J


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## jevansoh (Nov 12, 2014)

CharleyL said:


> You can stack saw blades if they both have the same number of teeth and are the same diameter. A dado blade assembled from one side blade and the 1/16 chipper with shims to get the spacing exact to fit your plywood would be the best way to cut accurate dados quickly on a table saw. If you cut some strips that are exactly 1 1/2 inches wide you can use them between the fence and the work, removing one strip for each pass. I would cut a dado in all of the boards, then remove one spacer and cut them all again, then remove another spacer, etc until all of the Dados have been cut. Tape or clamp the spacers in place to keep them from moving while making the cuts. This is an accurate way of getting the incremental spacing needed between the cuts. You don't move the fence at all. I hope I'm clear with this. If not, let me know and I'll try to describe it again.
> 
> Charley


I LOVE this idea and quite frankly it is my favorite idea so far because it won't require any measuring if I'm understanding correctly!

So "IF" I can figure out how to get the exact width dado I need for the nominal 1/4" stock I'll be using (seems to actually be .203" and not 3/16" like I originally thought) then I can just cut my thirteen 1.5" x 4' pieces first and use the actual pieces I've cut as my new "fence" position, removing one for each new dado. This should ensure accuracy that the 1.5" pieces will fit tight between each groove/dado since I'll be using the actual stock as my template.

So I'm back to figuring out what to buy to get a .203" dado, but I really like this idea because it's cheap, easy, no measuring, and nothing more to buy.

Any further suggestions?

THANKS!!

--J


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## jevansoh (Nov 12, 2014)

MT Stringer said:


> I used a pair of cheep 7 1/4 inch circular saw rip blades and a small shim or two to get the desired width. One pass on the table saw for each dado.
> 
> Might take a little thinking to come up with a spacing jig.


Do you mean you would use two Thin Kerf blades stacked together with a few shims from a dado set and that would be all I would need to make my dadoes?

If this would work and would get me to the roughly .203" dado size I need, then I can use the method in the previous post as my "jig."

I've also found a video on YouTube at youtube dot com /watch?v=f9MdXzCrTmU&list=PLkmV4CVyBSn63oSkBtq0kotOCpG6H4jl0&index=30 (I cannot post links yet so you'll have to "fix" this link to see what I'm talking about) called "No-Measure Evenly Spaced Dadoes" where the guy sets the fence just for the first dado, then uses just one spacer, and for each additional dado he simply aligns the previous dado back over the saw blade, puts the same spacer back in, locks the fence, and cuts the next dado. 

The video is only a few minutes long and explains it much better than I can in a few lines of text, but I would like to get everyone's opinion here as to whether or not this would be an accurate and good way of making my repetitive dadoes or if I'd be better off using the previous suggestion of lining up all 13 of the 1.5" pieces (roughly 2' worth) and just removing one at a time and sliding the workpiece over for each dado.

Or... If I should look more closely at a third option. 

Thanks again for all the great ideas and please keep them coming.

--J


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## jevansoh (Nov 12, 2014)

greenacres2 said:


> Sounds like the perfect job for an Incra LS system on a router table, using a 3/16" bit. Once you locate the center of the stock on the Incra system you could even change the bit size so that if you get a batch of 7/32" stock, you still get the same spacing between grooves.
> 
> Shoot, with a large enough table, the 32" Incra could handle doing the grooves in the 24" length across the 48" width. (the 25" could do the job in theory, but i'd not want to get that close to the limit of travel with accuracy being that important) Simply start in the middle and work toward the edges with each adjustment of the positioner. Easily repeatable system too.
> 
> ...


Thanks so much for your idea, but I have two concerns with this suggestion.

First, this jig is well over $300 and the table saw I'm thinking of buying is only $279, so it's a bit more than I'd like to spend. With that being said, if this does end up being the best suggestion, then I will just bite the bullet and make the investment.

Second, and most importantly, I've watched several videos on this system and read a bit about it, but since I don't own anything more than basic tools at this point and really have absolutely no experience, I'm afraid I honestly don't understand how I would use this jig easily to make 12 grooves 4ft long each in a 2ft wide sheet of MDF.

I just can't find any videos of this system doing dadoes or anything close to what I'm wanting to do and cannot visualize it due to my inexperience.

If you could point me to a video(s) and/or article(s) on how to use this jig to do the types of dadoes/grooves I want on large pieces and explain your suggestion a bit better I'd be very grateful.

Thanks,

--J


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## jevansoh (Nov 12, 2014)

DaninVan said:


> Hey, Jason; welcome!
> You didn't mention what your 2' x 4' panels are made of? MDF or plywood?
> If they're MDF you are going to be making a LOT of very nasty dust... please don't underestimate how bad this stuff is for your lungs. Plywood's not much better.
> An alternate system could be alternating the vertical 'fins' with 1.5" wide full length spacers, butted up tight to the fin and glued to the base panel. Tight fit and no dadoing required. make everything from the same 1/4" plywood.


Hi there, and thanks for your input.

I was planning on using a 1/2" or 3/4" sheet of MDF cut to 2ft x 4ft for the bottom, which is what will have the biggest amount of cutting, since there will be 12 grooves that are 4ft long each. However, this part won't actually be seen as it will be covered by risers and fins (there is a link in the very next post after your original post showing exactly what I'm building other than the dimensions - I cannot yet post links) so if another material would be easier to deal with and not too much more expensive, or better yet, less expensive, by all means please make a recommendation.  Thanks for your concern about the sawdust. I hadn't yet considered that. I'm looking for the cheapest and easiest method to building these and up till now at least, it seemed to me that MDF would fit the bill.

The fins will be 8" tall each (these are what will sit in the grooves) and I was just going to use 1/4" hardboard which turns out to be roughly .203" in reality. So the plan to make these was simply to buy a 4'x8' sheet, cut it in half to two 4x4 sheets, then rip each 4x4 sheet down to six 8" pieces, giving me the exact number (12) of fins I need in one full 4x8 sheet. Does this sound like the best method to you or would you do it another way and/or use a different material?

I was going to buy precut 1x2's to save time for the risers that go between each fin, and just nail them in at the top and the bottom, so no sawdust there.

So the only things I have to cut are the grooves in the bottom 2'x4' sheet and the dadoes in the top and bottom of the 8" x 2' sections so the fins will be supported on 3 sides.

I LOVE the idea of no dadoing required, but to be honest, I don't quite understand your suggestion.

Would you care to elaborate?

I'm looking for the fastest, not necessarily the cheapest, but the fastest and easiest way that unskilled labor (I want to make it as idiot proof as possible using jigs/templates so I could possibly even hire some neighborhood kids to help since I will be making tons of these) could produce these one the plans, jigs, templates, etc are all figured out.

I'd love to hear more about your idea for no dadoes and spacers, but if I understand what you're saying, wouldn't that take a lot more material and a lot more time?

Thanks,

--J


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## jevansoh (Nov 12, 2014)

boogalee said:


> Is this what you are trying to build.
> 
> If so:
> 1. Do you plan on buying a router?
> ...


YES!! That is almost exactly what I'm building. I cannot post links yet which makes it difficult to explain certain things so I appreciate you finding that.

The only differences with mine will be that it will be roughly 2' wide and will be 4' tall instead of square, plus instead of 7 wells/dividers it will have 13. But yes, that is what I'm building, and will be building a ton of them.

To purchase these devices, they range between $400-$600 each and I just cannot afford that, plus I can customize it and make a better one all while saving tons of money if I can just figure out the best jig/template/method to use.

I will have to purchase a table saw no matter what, in order to rip the plywood/mdf for the back and for the fins which will be 8" x 4' so I am hoping whatever solution we come up with will not require both a router and table saw at this time.

You're right, I didn't put anything in my profile yet because I haven't made my final decision.

If I have to buy a router, I honestly don't know what I'm going to buy yet.

I plan on purchasing the Porter Cable 6 gallon 150PSI 3 tool air compressor combo kit from Home Depot for $199 which will give me a brad nailer, finish nailer, and stapler which will help with assembly.

I plan on purchasing the Kobalt KT1015 Table Saw from Lowe's for $279 unless you guys think I could get something better for around the same price.

I will also be purchasing a digital micrometer, am looking for a package deal on mostly long (with a few short) clamps, as I have none, and was thinking of purchasing the Vermont American Wobble Dado blade since you can "dial in" the setting and it goes down to 3/16" where, according to the specs listed, all stacked dado sets only go down to 1/4" even though there has been a previous suggestion of purchasing a stacked dado set and using only one 1/8" blade, one 1/16" chipper, and some shims, in order to get to my necessary dado/groove width of .203" (The spec of 3/16" I mentioned before is incorrect) but I really need suggestions on what to buy.

IF I have to buy a router, I really don't know where to begin. I've spent a lot of time watching video reviews and reading reviews on the aforementioned items in order to narrow my list, but just don't know anything about routers, bits, and where to begin.

I currently have a 10" compound miter saw, a circular saw, jigsaw, hammer drill, regular drill, dremel tool, reciprocating saw, and other misc household hand tools that most homeowners have.

I really don't have anything else at all and don't know what else I'll need other than some type of sander but don't know what kind would be best for building these diffusers although I was leaning towards a random orbital sander.

Would it be appropriate to list all the items I already own (since they're pretty standard and nothing special) in my profile or is the above reference good enough for now until I make the bigger purchases mentioned above?

Thanks again for posting that link and I hope this answers your questions.

I look forward to your suggestions and recommendations and truly appreciate your time and effort in assisting me. It's fund to spend other folks money, eh? 

--J


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## jevansoh (Nov 12, 2014)

jw2170 said:


> Rockler Router Fluting Jig - Power Router Accessories - Amazon


I like that jig, but it is only for up to 8" x 9.25" I believe and my pieces are 2' x 4' so I don't see how it would work.

I can't visualize how I'd use it for what I'm building but if you think it will work for my 2ft x 4ft sized projects I'd really appreciate it if you could explain to me how I'd use it.

Thanks for your time,

--J


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## jevansoh (Nov 12, 2014)

old55 said:


> Welcome to the forum Jason


Thank you! I'm already enjoying my time here immensely and think I'll really learn a lot. I cant wait to look back at this, my first thread here, one day and laugh at how inexperienced I was and how far I've come.

My brain hurts from the amount of research I've put in over the last few weeks and the lack of sleep I've gotten, but in all honesty it's been fun, and I've gotten to meet you guys!

Thanks again,

--J


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## jevansoh (Nov 12, 2014)

Stick486 said:


> something the size of a Bosch Colt in a plunge base would be made to order for this...
> 
> Colt Palm Grip 5.6 Amp 1 HP Variable-Speed Combination Plunge and Fixed-Base Router Kit
> 
> FWIW... 3/8" is a might deep.. suggest you go for a 1/4"... or less


Thank you for the router suggestion.

Since I have been hoping to find a solution that would allow me to use a table saw since I "think" it will be quicker, easier, and cheaper since I wouldn't have to buy both a router and table saw at the same time (if I can figure out the narrow dado setup for the table saw), I haven't spent too much time researching routers.

Since I know nothing about routers, the bit of research I have done has only confused me more.

I got to the point where I thought I would need to make one of the referenced jigs and find a 1/8" or 3/16" bit with a bearing, then make two passes per dado, but cannot find any bits that small with bearings, and don't know anything about guide bushings or how to make the jig to accept that and still get the dado size I need.

I've never even held a router.  So... If the router method ends up being what I go with, I'd like confirmation from a few other forum members that this would be the best one to start with.

I was going to go with a fixed base and already I see you recommend a plunge router, so it's nice to have the expertise of the members here to correct me and guide me. 

BTW, point taken on dado/groove depth. The fins will be supported on 3 sides and will be 8" tall out of material that is actually .203" (3/16 was incorrect) so I'm sure 1/4" is more than enough as you suggest and hopefully that will make it easier on the bit/blade(s) and make for less sawdust.

You mention 1/4" depth "max"... What specifically would you go with to support 8" tall fins on 3 sides out of .203" thick material?

Thanks for the suggestions,

--J


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## CharleyL (Feb 28, 2009)

Jason,

Read the second half of my post above about making something to get the correct spacing with the table saw. Using some strips of wood the width of the space that you need between the dado cuts you stack them against the table saw fence. Position your work against this stack and position the fence to get your first dado positioned correctly. Make the first dado cut, then remove one strip from the stack and position the work against the stack to make the second dado cut. Remove another spacer and make the third dado cut, etc. until you make the last dado cut on your work. This is the most accurate and fastest way to do this with a table saw, but the spacer idea works when using a router too.

Charley


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## Stick486 (Jan 4, 2013)

make a "T" shaped guide that cues off one dado to guide the router for the next dado...


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## MT Stringer (Aug 15, 2012)

Here is an option for you to consider.

First, let me say that I am a new Sketchup user still in the "basics" learning stage. Some dimensions may or may not be accurate. Take it for what it is, a general overview pictorial of the description below.

This jig would require the following:

Router with plunge base
1/2 inch Porter Cable Style guide bushing.
1/2 inch Pattern bit
1/2 inch mdf.
Screws or glue or small nails to secure the spacers in place.

Remember, accuracy is up to you. The jig should be made as accurately as possible.

With all that said, here is what you would have to do to build the jig.

Cut the jig base to size. It is wider and longer so you will have a place to clamp the jig to your workpiece and bench.

Cut the spacers. They are exactly one inch wide x 24 inches long.

To mount the spacers to the jig base, use a 1/2 inch set up block to space the spacers exactly 1/2 inch apart. That will allow the guide bushing to move along each slot.

Once all of the spacers have been attached to the jig, use the pattern bit to route the slots completely through the jig base. Be careful and vigilant while making the cuts. Make several passes increasing the depth each time until the bit cuts through the bottom of the jig base. (Note: Support the jig base with scrap or something to prevent the router bit from cutting into your workbench.)

With this jig, you would simply place it in the desired location on your workpiece, clamp it so it doesn't move and rout away with your 3/16 or 3/32 or whatever bit you end up using.

By building this jig as described, you won't have to do anything except decide where to start. The bit will be centered in the bushing and your cuts should be accurate.

I spent a little while this afternoon drawing this thing because I figured it would be easier to show-n-tell than just tell. 

Good luck.
Mike


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## Artie1085 (Apr 25, 2011)

Jason

How about a different approach. I have concern with you being able to manhandle a 2ft by 4ft board on a table saw the size you are looking at. Consider the following :

1. Get your table saw (whatever brand you decide)
2. As per previous suggestions find a combination of blades that will give you the slot you need. You can probable use 7.25 or8.25 in blades since your slots will not be deep.
3. Build or buy two inexpensive sawhorses to support infeed and outfeed (the same hight as the saw you choose. 
4. Using a 2x4 ft piece of 1/2 in MDF find tyhe point about 6in from the right sideand set you fence at this point. 
5. Lower the MDF using the fence as a guide slowly down onto the spinning blade for a cut through the board. Without moving the board turn off the saw.
6. Lift the board off the saw and reset the fence 1.5in to the right, reset your blade hight for the depth of slot you decide on, turn the MDF over and cut a slot.
7. Cut a piece of the material you will be using for the baffles 4ft long and of a width equal to the depth of the finished slot minus 1/16in. If you can find a piece of aluminum of the correct thickness and width, that would probable be better.
8. Without moving the fence, turn the MDF back to its' original position and mark the underside for guides to fit the miter tracks in the saw. Cut two pieces of hardwook as runners and screw them to the side of the MDF you have just marked.
9. Glue this piece into the slot as a guide. Just like a very oversized "Oak Park" finger joint jig.
10. Screw the MDF to your sawhorses.

You should now have a stable "zero clearance large table to cut your groves. The first cut on each board will register against the guide and each subsequent cut will register by using the prior slot riding on the 4ft guide.

You only make tyhis table once and the miter guides on the bottom will enable you to relocate the table if you take it apart.


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## Stick486 (Jan 4, 2013)

Artie1085 said:


> Jason
> 
> How about a different approach. I have concern with you being able to manhandle a 2ft by 4ft board on a table saw the size you are looking at. Consider the following :


because of your post count the attachment or link didn't take...
could you try again....


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## darsev (Feb 3, 2012)

Mike's post got me thinking, and I started drawing up a modified sled that uses the box making jig concept. Sketchup pics attached. That way Jason can use a table saw assuming he can get the right size dado.

Jason,

the concept of a sled is a board that sits on top of the saw table. It has runners underneath that fit into the mitre slots so that it can only slide parallel to the saw blade.

If you add to the sled a strip that is exactly 1.5" to the right of the blade and is the same thickness and height as the dado you want to cut, you now have a relatively easily made jig that will allow an unlimited number of dado cuts. For the first cut, you slide the board tight against the strip and then run it over the saw. For the next cut, move the board to the right so that the cut you have just made sits over the strip, and then make the next cut. Just keep repeating until you have enough cuts.

I hope the drawings explain it better. Thanks for the idea, Mike. For a long term solution, I think Mike's router jig might be better as you are not moving the boards you are cutting. Moving a 4' board over a table saw will definitely need support on the outfeed end, and there is also a risk that you could be reaching over the top of a spinning blade which is a safety issue.

In the drawing, the grey bits are a table saw, and the orange bits are the sled jig. You would put your boards on the sled.

Hope this gives you some ideas.

I am also curious to know what you are doing with these acoustic baffles. If they do what I think they do, I might be making some myself. Acoustically, MDF will dampen the sound. I am not too sure about the hardboard you are using for the baffles though. I think acoustically, it may bounce the sound like glass. I have not worked with hardboard, but I have used ply as a reflector for PZM mics, and ply would be softer than hardboard from an acoustic point of view and that is why I am wondering how it will react. I regularly work a church auditorium that has a plaster wall on one side and glass on the other. There is a 10db difference left to right across the auditorium.

Darryl

PS I work in metric so the dimensions are in metric - just substitute your own.


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## OPG3 (Jan 9, 2011)

Jason, Please forgive me for just now seeing this post. I was referenced in the first post by Charles. My first thought is...Why not use a "fin" material that is truly 1/4" thick? This way you can use your preferred dado method without all of the gymnastics! It ain't rocket science to make equally-spaced dado joints: 
Cut all full size pieces + one to be slotted first. Then stack them up.
Set-up for dado slot number one and cut it into every piece. Stack these until all have one slot.
Set-up for slot number two and cut into every piece. Blah, blah, blah.

or, Save a lot of money and just pay someone (already equipped) to do it for you. Many sheet materials that call themselves 1/4" really are 1/4", but plywood is misleading!

Otis Guillebeau from Auburn, Georgia


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## MT Stringer (Aug 15, 2012)

After getting some well deserved sleep, I have modified my router jig suggestion.
As it turns out, the spacers are only necessary while the slots are being routed into the 1/2 inch mdf jig base. Cut as many as desired, but I would do all of them so the jig could be set up once per workpiece.

Remove the spacers and all that would be left is the "Jig Base" as I have it labelled.
Add a spacer to the front edge so it will register the jig properly and screw it in place.
Then carefully place the jig into the correct layout position on the workpiece. Measure and cut a spacer for one end so that it lines up with the end of the workpiece. 
Clamp it in position the same way for each workpiece being routed.

Note: I clamp the jig and the workpiece to my work bench so it doesn't move unexpectedly.

Here are a couple revised pics showing the finished jig.
Hope this helps. 
Mike


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## Artie1085 (Apr 25, 2011)

Stick 486 

Take a look at my edited post. The first one was sent in error.


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## jw2170 (Jan 24, 2008)

I would use a router with a home made base.

Screw a fence the correct size to the base at the correct offset from the cutter.

I have seen this on YouTube or in a magazine, but cannot find it...


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## jw2170 (Jan 24, 2008)

*slotting jig*

PS I found this in another post which explains what I meant.....VBG.


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## Dejure (Jul 27, 2009)

1) I'd make the guide a bit longer, so it protruded beyond the base, to better insure a parallel cut. I do this on my circle and other jigs and it helps greatly in the alignment.

2) By cutting two slots ninety degrees to the dados (parallel to the front and back of the base), you can have infinite adjustment in the positioning of the dado guide. You'd just set the dados up using, for example, a try-square, then lock them down.

You'd use standard jig T nuts or bolts and knobs that fit through the slots and are secured in the guide. 

If you wanted a more exotic guide, you could slot the guide too, so you could make slanted cuts, if desired.



jw2170 said:


> PS I found this in another post which explains what I meant.....VBG.


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