Cut longer than shank?

Can you make a profile cut that is deeper than the shank length of a bit? If so, what is the trick to avoid burning? I’m cutting wood.

I have a bit with a 3/4" shank and I’m trying to make a 1.5" cut. When the bit gets to the halfway point (beyond the length of the shank), it begins to burn, conceivably because the bare part of the bit is rubbing against the wood. Or is there another reason or way that I can avoid it?

I know that I can buy bits with longer shanks but I also want to make much longer cuts, so I’m looking for a way to make longer cuts with shorter shanks anyway. Is there a way? Is it a speeds and feeds thing (note the first half of the cut is perfect)? Or material clearing thing (trying to vacuum it out quickly, as it goes)? Or does it simply not work?

Is there a way to make this work?

Thanks!

Yeah in theory it should work, but if you have any runout the shank will hit and rub.

The quick answer is use a longer bit. This is why I have a 3 inch long 1/8" bit. Which I only use when needed as that long a bit has terrible deflection and runout issues.

One trick is to “Staircase” the profile cut. With each stage being just a little bit shallower than the cut length of the bit. You cut the top channel just a little bit wider than the bit so that when it cuts the next level there is some clearance for the shank.

Depending on the cut you can then sand down the sides after or leave them for a more stylized look.

But this kind of issues is why on some projects I use a 1/4" downcut bit to do the profile, instead of my 1/8" downcut bit. Because the 1/4 has a deeper length of cut for thicker material.

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Thanks everyone!

Sorry, I’m still learning the language. I’m new to the world of CNC.

Just to confirm… Are any of you guys using a bit with a cutting edge shorter than the profile you cut? And with no noticeable rubbing? I’m a little confused because I am reading that it is NOT possible, then that it is. That run-out will work in my favor and then against it. But I do understand the rationale in all cases. Seems to make sense.

My surface quality, aside from the recent (as I went deeper) burning seems to be really good, so I don’t think I have much run-out, but who knows? Bottom line: Is anyone cutting deeper than the cutting edge on a regular basis with no issues? Is this attributed to? (1) Lots of or very little run-out (2) Shallower passes than normal (3) Slower speed than normal? Etc.?

Or if it simply is not a good idea to us a shorter bit like this because no one has achieved reasonable results, please let me know (and I’ll reevaluate my options).

There are a lot of variables at play in CNC work. I’m really enjoying it but I feel like I walk right past the optimal setup a lot when I make the wrong tweaks to accommodate changing conditions.

Thanks!

I do it all the time and almost never have any “burning” issues. Probably not the best practice but I haven’t had any issues.

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Thanks guys!

@Stan: Ok. As long as it can work, I’ll keep adjusting my approach and see what I get.

@Robert: Oh, that’s an interesting idea. I’ll give that a try.

sometimes it causes problems

Ok. Thanks everyone!

Shank is my wife’s maiden name…

I came up with another solution by accident. I was just about to try slightly grinding down the shank of my regular 1/4" end mill when it occurred to me that I had a straight router bit (for my router table) with a wider tip (1/2") and narrower shank (1/4"). Similar to this:

I looked at it closer and realized it had a slightly pointed tip, so it could plunge (unlike the kind you see with two blades and a gap between). I decided to give it a try, with a conservative (2mm) depth/pass and it worked great! Surface finish was great and the 1/2" tip allowed me to hog the wood faster.

Now I’m looking at my other standard bits to see if I can use any of them too. I am going to try a v groove bit for v carving.

Thanks everyone for your help! The tips led me to my solution.

Oh, good to know. Thanks Phil!

I was going to try to lathe it, but I guess I’m glad I found the other solution. Ended up being better in many ways anyway.

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