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Looking for advise for which router bit for pattern cutting

5K views 12 replies 4 participants last post by  Shesho 
#1 ·
Hi,

I'd like to try some router cutting using a template. The set up would be table mounted.

So far I can see there are three choices,

Straight cutting bit (possibly with top & bottom bearings)

Shear cutting

Spiral cutting

I'd like to cut hard woods including stuff like maple and walnut, up to 3-4cm thickness.

The bits with double bearings look good so you can flip your piece to get a more suitable cut into the grain. How would this compare to a shear cutting bit? I dont think I can find any shear cutters which have a double bearing bit.

Spiral cutters are something I know the least about.

Any advise, or pointing to resources is very appreciated. Thank you
 
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#2 ·
Hi,

I'd like to try some router cutting using a template. The set up would be table mounted.

So far I can see there are three choices,

Straight cutting bit (possibly with top & bottom bearings)

Shear cutting

Spiral cutting

I'd like to cut hard woods including stuff like maple and walnut, up to 3-4cm thickness.

The bits with double bearings look good so you can flip your piece to get a more suitable cut into the grain. How would this compare to a shear cutting bit? I dont think I can find any shear cutters which have a double bearing bit.

Spiral cutters are something I know the least about.

Any advise, or pointing to resources is very appreciated. Thank you
A lot depends on what you are doing. With a shank mounted bearing the entire cutting length plus some needs to be exposed before the bearing guide can become effective. Tip mounted bearing bits obviously cannot be plunged. I also doubt you will find a spiral with a shank bearing. Spirals and shear cuts do very nicely across grain. I've also done some template work with guide bushings installed in the table.
In short, like most things, there is no "one size fits all". Would need to have a little more specific information to give a specific recommendation. :smile:
 
#3 · (Edited)
Generally a bearing mounted closest to the shank is for hand held work because the base of the router is sitting on the template. With your router table the bearing is at the end opposite to the shank because the router is now below the work and the bit has to follow the template which is still on top of the material being cut.

The bit you would look for is called a "pattern cutting bit".

A handy way to judge the cutting direction is to use your right hand as a guide.

For handheld work lay your hand beside the work palm down with your thumb touching edge of material and index finger pointing out. Index finger points in direction to make cut.

Using a router table lay right hand palm up, follow index finger direction.
 
#4 ·
Straight faced bits with the bearing next to the shanks are commonly called "pattern cutting bits". Straight faced bits with the bearing at the end of the bit are commonly called "flush trim bits". Either can be used in a handheld router or a table setup.

This might help with feed direction...
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#5 ·
Thanks for the replies.

I suppose what i'm concerned about is finding the best bit to reduce tearout and risk of kickback.

I can see the various options, these seem to generally known as flush trim bits. I'm a bit unsure of whether to get a straight or shearing bit.
 
#6 ·
There is an advantage to a shear type bit like this:
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Tool accessory Tool socket

The fact that the cutting edges are at an angle could get a cleaner cut. It's the same principle as a handplane held at a slight skew when using.

Feed directions are like this:
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Tool accessory Room Roof Metal Illustration

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The cut produced will be as your pattern is prepared. The smoother the better.





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#7 · (Edited)
Thank you.

I realise its the pattern cutting bits I want, not flush trim. The flush trim having bearing at the top.

Is it safe and okay to use a down shear bit in a table mounted router? I would imagine you want the shear to pull the workpiece down, upwards sound a bad idea, or are the forced not enough to worry about?

I think this may be the bit i'm after

http://www.rockler.com/product.cfm?page=16976&site=ROCKLER

Shear with an option for double bearing, though down shear.
 
#8 ·
Hi - That Rockler bit should do fine other than possibly being a little short. Your original post said you had 3-4cm stock. 4cm would be roughly 2". Likely not a big issue if you keep your template stock around 6mm. If you run out of cutting length, just raise the bit so the bearing rides on the freshly cut surface. At that point, if you needed even more, you could just remove the template.

As far as shear direction, up cut and down cut don't necessary mean up and down. Up cut means that the bit will pull the chips toward the collet and try to push the stock away. Downcut is just the opposite. Dynamic forces shouldn't be a concern with pushing the board off the table given a reasonably sharp bit and depth of cut. Depth of cut in this instance will be defined as the difference between the edge of the stock and the edge of the template. :smile:
 
#9 ·
Thanks =)

Found a very similar bit from a uk producer (im in uk)

http://www.wealdentool.com/cgi-bin/sh000001.pl?REFPAGE=http%3a%2f%2fwww%2ewealdentool%2ecom%2facatalog%2fRouter_Cutters_1%2ehtml&WD=shear&SHOP=%20&PN=Online_Catalogue_Down_Shear_Trim_23%2ehtml%23aT8175B_2d1_2f2#aT8175B_2d1_2f2

That one has a cutting length of 50mm but seems identical in nearly every other way. I'm still a bit unsure about the down shear and vertical forces, but you feel this would be fine when using a table mounted router system?
 
#10 ·
Thanks =)

Found a very similar bit from a uk producer (im in uk)

http://www.wealdentool.com/cgi-bin/..._Trim_23.html#aT8175B_2d1_2f2#aT8175B_2d1_2f2

That one has a cutting length of 50mm but seems identical in nearly every other way. I'm still a bit unsure about the down shear and vertical forces, but you feel this would be fine when using a table mounted router system?
The shear won't be an issue. I use a similar bit on my table regularly for doing edge jointing. You likely won't have to remove more than 2-3 mm per pass anyway. As always, you need to exercise due caution but I don't forsee it as an issue. :smile:
 
#11 ·
I plan to precut on a bandsaw. I guess I can manage 2-3mm within my template though it does sound like it'll take some concentration.

Suppose you can always use a hand file if you have any areas which you really struggle with or make multiple passes?. I also saw something called bump cutting to remove thicker areas which I could try.

Thanks for the advise. I will be being pretty careful as it looks quite an intimidating procedure at first, though pretty straight forward.
 
#12 ·
Bump cutting works fine, just nibble away at it. Don't get overly concerned if you are more than 3mm away from the template, just make an extra pass. Don't force anything.
 
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