Drilling printed parts

Hello all!

I am building Mendelmax 1.5 and I have a bit different aluminium extrusions so that plastic parts I have won't do. Actually, only thing I need to do is widen some 5mm holes in plastic parts to fit my M8 tapped holes in aluminium. Now, what is the best way to widen plastic part holes? Is it by drilling and which drill bit I need to use, or should I try melt and widen holes with soldering iron maybe? Parts are mostly PLA.
Anyone have some experience?

Thank you!

Niksa

Niska, it all depends on whether the parts were originally printed as solid fill or partial fill objects, as to how wide a drill bit you can use. You can definitely use a drill bit to do the job, but if they're not solid, the best bet is the avoid going much larger than the intended diameter, ie, essentially for reaming out poorly printed holes as cleanup. If solid, you can do pretty much whatever you like as long as it doesn't compromise the object itself.

You'll have a lot of trouble trying to widen the holes by heating or softening the plastic. Drilling is your best bet, although going from 5mm holes to 8mm holes may present a problem, in that you will be drilling into the infill. If the parts are reasonably solid (0.3 or higher infill) then it should work just fine.

If you do drill the parts, go slowly. PLA will heat up with friction of the drill bit and soften, causing it to grip the drill bit if done too fast.

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Actually, problems with machining plastics is seldom a result of going too fast.
You need a really, really sharp tool. Go with HSS as it's easier to get sharp than "better" materials, feed the drill into the material readily so it cuts well and not in a way that just wears the material away, Use a DIN 343 drill or the like that is suited for the application. A normal drill bit does not cut with its flutes on the sides. Pre drilling is seldom a good thing no matter what some old gurus say.

Try cooling with a spray bottle of water either plain or with some alcohol (ethanol) or some detergent in it. Don't soak the part. Pull the drill bit out of the hole entirely with intervals of a few mm to break the chips and minimize clogging.

Mostly when drilling with small drill bits like those in plastic materials (POM, PP, ABS) we just spray the parts with whatever coolant is in the machine with a high pressure and feed the drill as fast as the machining center can go into the material and "peck" with some 5mm intervals or so depending on the application.

Edited 1 time(s). Last edit at 10/12/2012 03:04PM by zboz.

Thank you all for replies.

I used 8.5 HSS drill bit and succesfully drilled holes in four solid fill lower vertex lower parts, but on lower vertex upper parts I had trouble widening part where M8 screw socket head is going. Also, widening 5mm hole into 8.5mm started breaking small parts all around, probably the infill wasn't 100% solid and the angle was trouble too.
To clarify again, my aluminium extrusions came with M8 tapped holes.
Here are some pics of what I have done:





Eventually, I fixed 340mm extrusions to lower vertex upper part only with two t-slot nuts from sides, but not with M8 screw and it seems quite stable.

"You need a really, really sharp tool."

That's basically it, although because heat is always generated, doing a deep drill in steps (both in terms of diameter for larger holes and in terms of depth of cut per operation) is best to reduce unexpected tearing. One does not need to use fancy drill bits or reams for the rough holes used for the M8 holes, regardless of what some naive young gun who relies on a bevy of exotic tooling says. (exotic from the perspective of the average person getting into this project who may have a drill bit set but doesn't have a tool cabinet full of reams, special purpose drill bits, etc.) Just sharp bits. Leave the fancy (reams etc) to precision holes that require tight tolerances. Most of these reprap pieces parts are far from rocket science...about as far as one can be, and cleanup can be achieved quite easily using a portable drill, a sharp bit, and holding the piece by hand while cleaning the holes

Obviously, significantly enlarging a hole into something with low infill (or any frankly) is a recipe for problems, since once you exceed the interior wall thickness of a column (ie, the column that wraps an extruded hole, you're into material that has no substantive integrity.. The best one can expect to achieve with these printed holes, presuming an average wall thickness of three or four extrusion widths, is a cleaning operation.

Edited 1 time(s). Last edit at 10/13/2012 12:06PM by xiando.