Pattern bit question

[BobA]

I noticed that there are pattern bits which will allow me to duplicate pieces of my cabinet using the cabinet piece instead of makeing a template.   There seem to be 2 different constructs of the same bits.  One bit has the bearing at the top and the other has it at the bottom.  I have been going over the pros and cons without actually trying them so I wonder if someone with experience with these bits can give a brief pro and con of where these 2 types are used.

Thanks

[javeryh]

You want the ball bearing on top.  The other one is a "flush cutting bit"

[fixedpigs]

i have yet to get a pattern bit...i need to...
i always used my flush trim bit(bottom bearing) for any pattern work i needed...it'll get the job done...but it's more of a pain than a pattern bit would be...

[BobA]

Thanks for the quick response.   That means I need a pattern bit with the bearing at the top and a cutting edge that is about and 1 1/4 inch to trace a 3/4 thick piece onto another 3/4 piece.

[ScottS]

Thanks for the quick response.   That means I need a pattern bit with the bearing at the top and a cutting edge that is about and 1 1/4 inch to trace a 3/4 thick piece onto another 3/4 piece.

Actually, the cutting length only needs to be 3/4" long; you don't need to cut the piece you're trying to duplicate, after all! As a whole, the bit needs to be long enough so that the bearing can slide along the template piece.

[javeryh]

The pattern bit I have works great for making up to 3/4" copies of whatever.  My patterns range from 3/4" thick (if I'm matching sides of an arcade cabinet) to 1/4" thin (I have a few templates for furniture).  I also use my pattern bit a TON for making straight cuts.  I've attached a pic of how I use my bit.  The piece of wood with the grain is the "pattern" for the MDF I'm cutting (I'm making a straight cut here).

[BobA]

If your pattern is 3/4 thick can you extend the bit down to cut the new 3/4 in one pass.  I guess the question is the shank of the bit long enough so that the cutter gets down to the bottom of the new 3/4 when you are on top of the pattern 3/4?

If I understand right you just need 3/4 for cutting with a shank on the bit long enough to let it go down 1 1/2 when I use one side as a pattern for another.

[javeryh]

If your pattern is 3/4 thick can you extend the bit down to cut the new 3/4 in one pass.  I guess the question is the shank of the bit long enough so that the cutter gets down to the bottom of the new 3/4 when you are on top of the pattern 3/4?

Yes.  Easily - that's what they are made for.

If I understand right you just need 3/4 for cutting with a shank on the bit long enough to let it go down 1 1/2 when I use one side as a pattern for another.

I'm not sure I understand what you mean but the shank of the router bit ALWAYS goes in the router all the way all the time.  It's dangerous to only put the bit in 1/2 way or something to get a little more depth (I learned that the hard way and thankfully no one got hurt when my bit went flying).  The shank lengths are probably universal so I don't think you could find bits with varying shank lengths. 

If you wanted to use it to cut out a pattern in a piece of wood say 2" thick or something you would just make it in multiple passes.  The ball bearing would eventually rest on the piece itself (not the pattern) the deeper you went.   

[ScottS]

If your pattern is 3/4 thick can you extend the bit down to cut the new 3/4 in one pass.  I guess the question is the shank of the bit long enough so that the cutter gets down to the bottom of the new 3/4 when you are on top of the pattern 3/4?

If I understand right you just need 3/4 for cutting with a shank on the bit long enough to let it go down 1 1/2 when I use one side as a pattern for another.

You realize that all routers, even fixed base routers, allow you to control how much of the router bit is exposed beneath the base, right? And that any template bit with a 3/4" cutting length will be 2+" in overall length? So, you put the bit in the router, set the router on the template, and then adjust the router bit so that the bearing rides along the bottom edge of the template and the cutter is making a pass across the entire width of the material you're cutting. Having a cutting surface that's slightly longer than the thickness of the material (e.g. 7/8" or 1" when cutting 3/4" material) makes the setup process slightly less fiddly.

Of course, what most people do is make their templates out of thinner material than the final product. That makes the template cheaper, lighter, easier to move and store, etc. 1/4" thick baltic birch plywood is a great material for templates!

[BobA]

Thanks ScottS and javeryh  I have been having a bit of brain damage going on.  My router has been mounted in a table for so long I forgot what it looks like.   Now I remember the depth adj etc.   I was thinking of my dremel which of course does not adjust for depth which I used about 1 year ago.   It has been alot longer since I unbolted my router from the table its mounted in.

Sorry about the memory lapse guys I guess I should use my tools more often.

My biggest problem in using some of them is finding them so I can use them.

 

[Mallen]

Javeryh, actually the manufacturer (porter cable and delta) recommends that the bit be bottomed and then raised 1/16 inch before tightening.  This is because as your tightening the bit, it moves down and squeezes, but if the bit is already on the bottom, I may stop before there is a good squeeze.  Make sense?  Also, I've heard that heat can transfer from the bit to the motor if bottomed out.  But you are right, the placement of the bit should never be used to adjust bit height.