# trepan tool for mill



## DMO (Jan 25, 2012)

I'm thinking about an alternate method of cutting holes through 1/4" to 3/4" plastic instead of holesaws. I've tried cutting out some of the teeth of a standard holesaw so the gullets can handle more, and though they work better, they don't perform as well as hoped. I've tried one of the 3-tooth carbide holesaws with a tall slot for a gullet, but the teeth are so wide (~3/16") that it seems to require too much effort, and chatter gets really bad. 

Has anyone had any good experiences with any of the lesser expensive trepanning tools (not the really cheap ones) that use either one or two cutters that can be ground fairly thin?
Dave


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## British Steel (Jan 25, 2012)

Hi Dave,

To help the holesaw clear the chips, drill a hole in the waste so it gives 'em somewhere to go - stops it clogging and makes the cut go a lot better.

For the softer plastics (HDPE, PTFE etc.) I use a Forstner woodworking bit, goes through pretty quickly and gives a reasonable finish (would need cleaning up with a boring tool if cosmetics/surface quality mattered). Gives great plastic streamers too 

Dave H. (the other one)


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## Tony Wells (Jan 25, 2012)

You probably could make one, but I have used these with great success:

http://www.jancy.com/index.cfm?fuseaction=products.showProducts&cat=27


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## DMO (Jan 26, 2012)

Mainly my problem is the plastic loading up in the teeth and welding on.  This can happen within about 3 (slow) revolutions if I don't back out  and clear it. Usually I'm doing hole diameters from 1 to 4 inches  diameter in plastic up to 3/4" thick, sometimes even larger diameters,  and thicker plastics. On thinner stuff the teeth aren't buried much  below the surface, so I can be more patient because the work is soon  done, but once the shallow waste of a standard Bi-Metal holesaw sink  below the surface, about 3 revolutions of good cutting is all you get  before having to clear it. 

On a standard holesaw, I remove some teeth leaving the alternately set  ones(about every third or fourth one), then I sharpen what remains.  I  make a huge waste gullet between the remaining teeth which affords more  depth and dwell time before having to clear. I think whether or not the  teeth are widely set, the chips are able to float onto the sides and  scrub anyway, and then they melt and weld on. This is even with  compressed air, water, soap, etc. So I was attracted to the huge  cemented carbide cutter design which would seem to counter this action  and be a little more self-clearing. The ones I have found so far are all  very thick and require a lot of pressure, more than I expected. Heavy  pressure is bad for exiting the work, and it requires a heavier setup  all around. Sandwiching the material would help prevent breakage, but I  do a lot of symmetrical arrays designed to allow me to both flip and  rotate the work to make multiple use of each current setup position, and  additional materials can complicate things.

So, what I am hoping for is a compact but sturdy trepanning tool that  can allow me to insert a common but specially ground-by-me tool bit that  will remain stable throughout the operations, and preferably one that  will produce a self-clearing chip. I would love it if I could have that  in a single cutter tool so that I didn't have to fuss when adjusting the  diameter. Hmm, sounds like a boring head.
A boring head would only work if the setup is rigid and doesn't require the use of a pilot. 

It would also be nice if I could have this large-deep-hole cutting  functionality with a portable drill, which seems to suggest a 3-cutter  design. I've had one of those scroll adjusted 3-blade "holesaws".  They're small, weak, and loose, so I don't think much of it for  repeatable work. For one-off shallow cuts, maybe good until dulled. If  there was a more sturdy one like that, .... it could work.... I  wonder.....
Dave


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## Tony Wells (Jan 26, 2012)

For the larger sized holes, you would probably be better off using a boring head with a hand ground trepan bit. I've seen those 3 blade saws, for wood work. I never thought much of then, really.


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## DMO (Jan 26, 2012)

I wonder if there is a clever way to adapt one of these two-bit type circle cutters so that the cutters remain self-centering while adjusting the diameter setting?
Dave

View attachment 33056


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## Tony Wells (Jan 26, 2012)

You could make up some setting blocks in pairs, once you got it set. One fit between the main arbor and the cutter holder on each side. Mark them and use them to set up. Otherwise, it would be a case of a matching LH and RH threads, like parallel clamps or a turnbuckle.


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## DMO (Jan 26, 2012)

Tony Wells said:


> You could make up some setting blocks in pairs, once you got it set. One fit between the main arbor and the cutter holder on each side. Mark them and use them to set up. Otherwise, it would be a case of a matching LH and RH threads, like parallel clamps or a turnbuckle.



Yep, that's what I was thinking about. The LH/RH threaded shaft could float through a captive knob and the initial centering could be locked in place with a setscrew in the knob. The tool holders would be improved or replaced to hold a about a 3/16" or 1/4" square HSS tool bit ground on one side only, or the centering adjustment could be readjusted once to accomodate unique toolbits.

Hmm, maybe a silly idea.

Dave


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## Tony Wells (Jan 26, 2012)

It's probably a workable solution, but I can't tell from here if the thing is rigid enough to do the job. I would guess that for the larger diameters, it might be a little light.


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