# spiral bit for cutting plywood



## calneva (Sep 27, 2017)

I am cutting 23/32" hardwood plywood with a router. Some of the cuts for example are 33", 22", 15", 10" and 5" diameter circles, and curves with similar radii. I estimate that I cut about 500 lineal inches out of a 4'x8' sheet, and up to two sheets per week. I use a Porter Cable 7539 with a radius jig and with templates I have made.

For cutting, I've been using a Whiteside spiral compression bit, a 1/4" with two flutes: part UD2102. I bought it because it was less expensive and could do what I needed. After cutting a few thousand inches with it, it has worked acceptably but I wonder if I could do better with a larger bit.

I cut the 23/32" in one pass. With the 1/4" bit, I'm getting about 36 inches per minute.

I'm wondering if I go to a larger 3/8" or 1/2" bit whether I will be able to get a higher feed rate and whether this will still work well for hand-held use following a template. The wider bit will chew more wood and will require more torque from the router, but I think the 7539 will provide that. But will it feed faster?

With two flutes, the finish is acceptable. Will 3 flutes feed faster or just provide a better finish?

I think the up/down compression bit slows feed because chips get crammed between the up and down sections. A up cut or down cut bit might have better chip ejection and feed better but I'm concerned it will tear-out the veneer. I haven't tried it so I don't know.

I see the "ultimate compression" bits with extended up-cut flutes to improve chip ejection, but they are chamfered from a 1/2" shank to a 3/8" cutting width. That would make the depth setting very particular and it could complicate my use of templates. I would have to use a 1/2" guide but get a 3/8" cut, so my templates would have to be sized to compensate. I've got enough to think about that I don't think I want to rework the templates. I think the "ultimates" would work great with CNC, but my production volume would have to increase ten-fold before I go CNC.

So I'm thinking either a 3/8" or 1/2" compression. The claims regarding the ultimate compression bits suggest 3/8" is optimal for sheet goods because it takes less power than 1/2", but they don't compare it to 1/4" which should take even less power. So I'm wondering if there is any improvement to be had at all.

Is the UD2102 the best bit for my purpose or will a 3/8" or 1/2" bit work better?


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## Stick486 (Jan 4, 2013)

one pass cut w/ a ¼'' on plywood is a bit much on the bit....
rough cut your plywood w/in 1/8'' w/ a jig saw 1st and finish cut w/ a larger dia bit w/ 3 or 4 flutes.....
now you'll see a marked increase in speed of cut and no threat to power.....
cleaner too...
there's nothing like a bosh Progressor blade for your jigsaw......
suggest a T101AO...
a 3¼HP will push any bit you want...


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## DesertRatTom (Jul 3, 2012)

Downspirals give a nicer edge in ply. I use a DadoWiz for dados and grooves, especially stopped dados. I use the half inch version because the Wiz is set for exact fit cuts, and the half inch takes a big bite. The Wiz works on a track, so I can make several passes. A Bosch 1617 is what I use, and it has sufficient power. I now use high speed steel rather than carbide because the corbide is actually quite fragile. I'm more interested in the quality of the cut than speed. There is a big difference in finished results between HD crumby ply and Baltic Birch. 

If speed is the issue, not clean cuts, then I think 3/8ths will get you there fast. The half inch will hog out more material in one pass though. I've used two flute bits for dados, but it didn't produce a clean enough cut to suit me. 

I think the power of your router is going to be a factor as well in choosing between 3/8 and half.


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## Stick486 (Jan 4, 2013)

Tom...
the OP is cutting circles not dadoes in ¾ ply, using a 3¼HP router and doing it in one pass..
steel bits wold be a poor choice as he's seeking clean cuts, higher feed rates and wants longevity... not to mention he's cutting something like a 1,000LF a week...
in fact, precutting and using a down shear helix pilot bit would do him well...
Freud Tools


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## JOAT (Apr 9, 2010)

Stick486 said:


> one pass cut w/ a ¼'' on plywood is a bit much on the bit....
> rough cut your plywood w/in 1/8'' w/ a jig saw 1st and finish cut w/ a larger dia bit w/ 3 or 4 flutes.....
> now you'll see a marked increase in speed of cut and no threat to power.....
> 
> ...


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## hawkeye10 (Jul 28, 2015)

If you have a band saw make a circle cutting cutting jig for it. You will be able to cut circles at least twice as fast. 

Check on You Tube for ways to make a jig. Pick the jig that you like the best. They are easy to build.


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## Stick486 (Jan 4, 2013)

hawkeye10 said:


> If you have a band saw make a circle cutting cutting jig for it. You will be able to cut circles at least twice as fast.
> 
> Check on You Tube for ways to make a jig. Pick the jig that you like the best. They are easy to build.
> ]


excellent...


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## MEBCWD (Jan 14, 2012)

Looks like what you are trying to do is have a good finish cut on both sides of the circle by using the compression bit and don't want the extra tools. Using the 3 1/4 hp router you should have plenty of power for a larger bit.

I don't recommend using a large down cut bit in a handheld router because it could grab a hard spot and come up out of the work piece causing damage to the project and possibly the operator. Up cut bits can cause a similar problem when the part is cut loose and pull the part up the bit. Compression bits would be safer but caution is still advised especially using larger bits. 

Most of your 3/8" compression bits will be 3/8" shank so you would need a 3/8" collet for your router, I would not recommend using a sleeve. That should not be a problem finding a 3/8" collet for that router.

If you want to use a 1/2" bit you could use a Whiteside UD5202 or Onsrud 60-127MW both should give you good cuts on both sides of your parts and have decent cutting lifetime with the possibility to be resharpened by a good CNC sharpening service. You should be able to cut a little faster with the higher chip load of the bit but you need to remember the bigger the bit the more aggressive the cut and you need to make sure your jigs will handle the change or you might have big problems on your hands.


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## Dalton cnc (Sep 27, 2017)

Hows it going 


so yeah I think if you are only doing 2 sheets a week you should actually slow the process down a little so your less taxing on your tooling 

pushing a 1/4" compression at full depth at only 36ipm is causing alot of heat do you find that the saw dust is really hot when you are done? 

Personally I would stick with the 1/4" tool so you can maximize your material and take the depth in 2 passes just remember to go below the upcut length of the tool 

I think that you will find that you can get the job done faster, achieve longer tool life, and router life

what rpm are you running the router at? if its full bore you are dramatically shorting the life of your router 

and since its not a spindle with a vfd you will loose torque when you lower the rpm so you should run the router around 16k rpm and run a .375" depth of cut per pass 

you could even quickly blow the packed chips out of the circle as you plunge the router down for the second pass 

or better yet attach a air line to the router as you are cutting to blow the chips out


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## Cherryville Chuck (Sep 28, 2010)

A compression bit would be ideal if you jigsaw out the blanks first, staying close to the line. Two steps sound slower but I find it's as fast or faster. I have also made a jig for bandsaw and they are pretty fast but you'll still need to precut blanks. In this case don't cut close to the line leave 3/8 to 1/2" maybe. Cutting too close to the line will cause more pressure on one side of the blade than the other and may cause the blade to wander or cut at an angle.


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## DesertRatTom (Jul 3, 2012)

Sorry, misread the original post. I use a circle cutting jig on the band saw for this kind of task. Goes fairly fast.


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## subtleaccents (Nov 5, 2011)

hawkeye10 said:


> If you have a band saw make a circle cutting cutting jig for it. You will be able to cut circles at least twice as fast.
> 
> Check on You Tube for ways to make a jig. Pick the jig that you like the best. They are easy to build.


This would be good so long as he has not nested different diameters in close proximity to get the best yield from the sheet.


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