# Finding the bit centerline



## FreeTime (Dec 2, 2012)

In a recent mini-project, I ran into a few new (for me) challenges that I’m looking for better solutions to. I needed to make multiple cuts on the same centerline with a bit change in between (i.e 2 pass T-slot, cuts of different sizes on opposing faces of the same piece). 

I have a router lift so I’m changing the bit from the top and had to move the fence for access. In preparation, I added a micro adjuster to the fence just in case and what I thought would be a good idea for a repeatable setting on the fence (photo). (Position the fence, move the removable blocks and lock downs in place. When I needed to change the bit, take the moveable pieces out, leave the lockdowns untouched and reset the fence when done). I think the fence relocation blocks worked as I needed them to, as visually evidenced by the T-slot cuts (on another piece, not shown). 

Problem: (on the piece in the photo) I did not cut the bottom channel on the same centerline that I previously I drilled the some through holes. I’m attributing this to a bad RT setup. I usually try to find the outer edge of the bit and use the bit diameter but I’m not always reliable with this as it is sensitive to rotational orientation. You may be able to see it in the photo, the cl of through slot is not co-planar to the channel … it may be off 1/32" I’m guessing. I have no real way of measuring it but it is visually noticeable.

Sequence of processing: 
1. Roughed out the through 1/4" through hole on centerline (drill press) from the top. 
2. Cut the bottom channel (3/8”) on the RT
3. Clean out the 1/4" through slot on the RT.

I did it in this order because I thought I would clean up / minimize any drilling tearout in the channel, with the channel cut – hindsight, I’ll probably do it in the reverse order next time.

I probably need better eyes or better measuring equipment. What reliable methods have you used to determine the bit centerline to fence setting and/or retain the fence position between bit changes?


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## Nickp (Dec 4, 2012)

Mark...I use a flat steel rule across my two fences and look from overhead...adjust fence until edge of rule is over center of bit. Even though I change bits above table, I still need to move fence to take insert out. If you have a split fence you might be able to open them up wide enough and be able to remove insert and bit without moving the fence once you have it set.

For cuts like yours where the entire bit is away from the fence I use calipers (depth mode). You could also use something like THIS...


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## tomp913 (Mar 7, 2014)

If I'm trying to pick up an existing feature - e.g. the 1/4" hole drilled on the DP - I chuck up a piece of 1/4" dia drill rod in the router, set the part over the drill rod and then move the fence until it's tight against the part. Remove the drill rod and replace with the larger bit needed for the groove and they should be centered.

I also use the drill rod if I'm trying for a specific offset of the bit from the fence as it's much easier to measure to the drill rod than trying to pick up the high point on the router bit. So, if I'm trying to cut a 1/4" groove that's 1/2" above the edge of the part, chuck up the 1/4" drill rod and use the Wixey to move the fence so you have 1/2" to the outside (furthest from the fence) - or a 1/4" brass bar between the fence and the drill rod.

Tom


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## Cherryville Chuck (Sep 28, 2010)

That's not a job for a router table. You should be using a plunge handheld. Any jig that centers the router for the groove will keep you centered even if you change bits.


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## FreeTime (Dec 2, 2012)

tomp913 said:


> If I'm trying to pick up an existing feature - e.g. the 1/4" hole drilled on the DP - I chuck up a piece of 1/4" dia drill rod in the router, set the part over the drill rod and then move the fence until it's tight against the part. Remove the drill rod and replace with the larger bit needed for the groove and they should be centered.
> 
> Tom


I like the idea, in this case it would have worked but I'm not sure how I would apply this to any size other than 1/4 or 1/2 which the collets would handle


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## DaninVan (Jan 1, 2012)

"...I would apply this to any size other than 1/4 or 1/2 which the collets would handle."
I thought you were looking for the centre-line?
If yo chuck up a piece of 1/4" or 1/2" rod in your drill press, and file or grind a point on one end while the DP is running, you'll have a precise ctr. point when you put it into your router collett. Why would you need a different size other than those two?
But in any case, what Charles said about a jig.


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## FreeTime (Dec 2, 2012)

Cherryville Chuck said:


> That's not a job for a router table. You should be using a plunge handheld. Any jig that centers the router for the groove will keep you centered even if you change bits.


I agree, that would have been preferable for visibility and for repeatability between bit changes but I generally have a harder time rigidly fixturing small pieces with enough stability and access to use the plunge router with the guides. 

I have 2 DeWalt edge guides (bought one, inherited one) that I generally use in an opposing setup on one router that keep the router on track (for material less than about 8" wide) but there was not enough material here (length or height) to make this work - maybe I need another method of holding the piece / guiding the router. I do have a dado jig (too big) and slot cutting panel/jig that I use with a 1" template bushing (also too big).

There would still be some uncertainty on exactly where bit centerline is - off by a little and I would notice it when I flipped the piece over to work the other side (assuming I forgot to NOT flip the edges - a mistake I have to make about 3 more times to learn not to do it anymore)

Perhaps I should stop thinking / working from centerline locations and start viewing the things relative to cutting edge but that's more math than I like.


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## FreeTime (Dec 2, 2012)

DaninVan said:


> "...I would apply this to any size other than 1/4 or 1/2 which the collets would handle."
> I thought you were looking for the centre-line?
> If yo chuck up a piece of 1/4" or 1/2" rod in your drill press, and file or grind a point on one end while the DP is running, you'll have a precise ctr. point when you put it into your router collett. Why would you need a different size other than those two?
> But in any case, what Charles said about a jig.


Thanks - I missed the part about putting a point on it


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## tomp913 (Mar 7, 2014)

DaninVan said:


> "...I would apply this to any size other than 1/4 or 1/2 which the collets would handle."
> I thought you were looking for the centre-line?
> If yo chuck up a piece of 1/4" or 1/2" rod in your drill press, and file or grind a point on one end while the DP is running, you'll have a precise ctr. point when you put it into your router collett. Why would you need a different size other than those two?
> But in any case, what Charles said about a jig.


Or, you could use something like this http://http://www.eagleamerica.com/product/v400-1199/eagle_originals Somewhere in the shop, I have one like this except made out of steel, not sure where I bought it any more.


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## DaninVan (Jan 1, 2012)

Tom; for some reason I can't open your link. Does it work for you?


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## tomp913 (Mar 7, 2014)

Not sure what happened. Try the one below or paste the following in your browser Eagle Originals - Universal Brass Centering Pin

http://www.eagleamerica.com/product/v400-1199/eagle_originals

Tom


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## DaninVan (Jan 1, 2012)

Ooooh...nice find, Tom!
That bottom link is still bad but your 'browser link' just needed to be clicked on...no pasting required.


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## Cherryville Chuck (Sep 28, 2010)

You have probably been dropping the board onto a spinning bit if you have been doing it on a table and that is something I try to discourage people from doing. Besides being potentially dangerous, it's hard to keep the board steady while you are pushing down and you usually wind up with poor results. A plunge router was made specifically for jobs like this. If you put as much effort into figuring out a way to do this with a plunge as you have trying to do it your way you'll come up with a solution. If you have to move your fence to change bits then it will only be by luck that you get the second cut exactly where you want it.

If you use a jig and you need to cut from both sides then you don't want to flip your board over, you want to flip it end for end. This will register the same edge of the board against the registration point on your jig. Your slot may not be dead center but the second one will be directly on top of the first one.


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## vindaloo (May 30, 2009)

Personally I'd do the groove first on the RT, then double sided tape the stock to a sacrificial sheet of MDF (I have my bench covered with 6mm MDF for this purpose) towards the front edge of the bench. Then, using the same bit the groove was made with, set the plunge router edge guide so the bit fits into the groove and rotates without grabbing (using my hand to rotate it with the router UNPLUGGED).

Once the edge guide is set, replace the bit with the smaller one for the through mortise.

Then align to where one end is and clamp a stop block, then move the router to the other end of the required slot and place another stop block. Now set your depth and away you go.


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## Nickp (Dec 4, 2012)

This is my jig of choice for slots in small pieces, angled slots, etc...

I am not comfortable yet dropping a small piece onto a bit so this holds the piece, somewhat like a mortising jig and clamped to a vice. My trim router fits exactly in the space and I can add small blocks to set the travel.

To make slots in line with the piece I use a square for alignment...likewise for angled slots (like louvred shutters)

Hope this helps...Nick


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## Herb Stoops (Aug 28, 2012)

All good information here. I found the center of the collet a long time ago and marked it on each ends of the table , now I just set the fence on it , measure off it to set off sets.

Herb


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## FreeTime (Dec 2, 2012)

Cherryville Chuck said:


> You have probably been dropping the board onto a spinning bit if you have been doing it on a table and that is something I try to discourage people from doing. Besides being potentially dangerous, it's hard to keep the board steady while you are pushing down and you usually wind up with poor results.


No, I wouldn't do that - I'm not that brave or lucky. I hogged out the slot on the drill press and just cleaned it up on the RT. I did start it (the router) with the bit in in place in the slot with a slightly oversized hole which was bad enough.


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## AzOwl (Jan 25, 2015)

TomP...
The problem with your links is that they start with "http://http://

remove one of them and it should work but like it is redirects to a site with a rating as a possible malware site.


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## tomp913 (Mar 7, 2014)

*Problem attaching Link*



AzOwl said:


> TomP...
> The problem with your links is that they start with "http://http://
> 
> remove one of them and it should work but like it is redirects to a site with a rating as a possible malware site.


Al,

I saw that and tried deleting the first one but that didn't seem to help. When trying to insert a link, I copy it from the site, click on the appropriate icon and then paste the link into the box that shows up. At that point, you can see the extra http:// and I deleted the first. The time that I got the link to work, I pasted it to the body of the message and then tried using the icon method - the link I pasted became active and the other not. Guess I need to play with it a little more to see what's going on.

Thanks,

Tom


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## N'awlins77 (Feb 25, 2011)

Thanks for that link Tom. I ordered the brass centering pin and also the 4 piece quick corner package I found at that Eagle America sight, a couple of days ago.


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## chessnut2 (Sep 15, 2011)

Nick......I like the looks of that jig. You have any drawings and how to use it? Jim


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## tomp913 (Mar 7, 2014)

N'awlins77 said:


> Thanks for that link Tom. I ordered the brass centering pin and also the 4 piece quick corner package I found at that Eagle America sight, a couple of days ago.


I have this set and have found it to be very useful Corner Radius Template Guides, 3-Pc. Set-Carbide Router Bits | Router Bit Sets | Shaper Cutters | Saw Blades | Planer Knives | Jointer Knives | Infinity Cutting Tools

I make utility doors for my shop from a face frame with the back face rabetted to suit a plywood or hardboard panel and they let me cut a tight fit for the radius in the recess.

Tom


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## N'awlins77 (Feb 25, 2011)

tomp913 said:


> I have this set and have found it to be very useful Corner Radius Template Guides, 3-Pc. Set-Carbide Router Bits | Router Bit Sets | Shaper Cutters | Saw Blades | Planer Knives | Jointer Knives | Infinity Cutting Tools
> 
> I make utility doors for my shop from a face frame with the back face rabetted to suit a plywood or hardboard panel and they let me cut a tight fit for the radius in the recess.
> 
> Tom


Oh wow, like those even better!!


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## BrianS (Nov 7, 2004)

tomp913 said:


> Al,
> 
> I saw that and tried deleting the first one but that didn't seem to help. When trying to insert a link, I copy it from the site, click on the appropriate icon and then paste the link into the box that shows up. At that point, you can see the extra http:// and I deleted the first. The time that I got the link to work, I pasted it to the body of the message and then tried using the icon method - the link I pasted became active and the other not. Guess I need to play with it a little more to see what's going on.
> 
> ...


I just went in and edited it for you. It works now.


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## tomp913 (Mar 7, 2014)

BrianS said:


> I just went in and edited it for you. It works now.


Thanks Brian. I've posted a couple of messages with links, deleted the "http://" that's already in the box before pasting the link I've copied and, knock on wood, that seems to be working for me now. Hopefully I'll get it right in the future.

Tom


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