Deformed plastic gear on milling machine

[JasonBModerator @jasonb]

Thanks for the update Bill. I’m no 3D printing expert but by the looks of the surface I would say that has been produced by laser sintering or multi jet fusion not the hobby extruded filament so should be stronger.

[Bill PhinnParticipant @billphinn90025]

Thanks for the reassurance on that score, Jason.

Things aren’t totally straightforward at the moment. Although the file specifies 20mm for the bore, the gear I have from the printer has a bore of only 19.8mm. There is no way this will slide on to the mill’s gear shaft as is.

I set things up to bore out to 20mm on my lathe, closing the chuck jaws (gently!) on to the teeth of the smaller cog and pushing the big cog flat against the jaw faces, but encountered a problem: I couldn’t get the gear to run concentrically because the narrow gripping surfaces of the jaws on my 3 jaw chuck don’t all align with a gear tooth, but rather one jaw always wants to grip between two teeth. I’ve tried using the aluminium jaw covers I made for my four jaw, but it still won’t run concentrically. Needless to say, I didn’t attempt any actual boring.

I’m going to try the four jaw when I have time. Any tips meanwhile on how to hold a nylon gear for boring on the lathe would be appreciated.

[RobCoxParticipant @robcox]

Put some sacrificial material (plastic, ally) in the lathe, bore a recess so its an interference fit on the tips of the gear teeth. Tap the gear home, bore the ID. Make sure youve got a means of tapping the gear out afterwards. Job done!

[DC31kParticipant @dc31k]

Better the bore was too small than too big. 3D prints exhibit shrinkage in the same way that cast iron items do. If this were a production item, you would do some test pieces and tune the dimension until the finished piece was correct.

Make a 20mm diameter D-bit and ream out the gear’s bore. It is made of plastic. Mild steel would do for the tool.

A 20mm dowel pin or 20mm silver steel would be adequately close to the correct diameter if you did not want to do any turning work, meaning you only need to file or grind the end.

—

As above, make a sacrificial fixture. Cut a circle of 18mm plywood with a hole saw. Hold in external jaws in three jaw. Bore hole that matches OD of gear. Mark plywood and chuck jaw so it goes back into the chuck the same way. Put sawcut in plywood ‘washer’. Push onto gear. Resecure in chuck.

[Bill PhinnParticipant @billphinn90025]

Many thanks for the helpful replies.

I’ll try making a fixture out of something suitable and see how things go.

One of my first thoughts when I found out the bore was undersized was that this was better than oversized.

Ideally, I’d like to have my old gear back from the print shop to gauge what fit to aim for (a tight, sliding fit is all I recall) when boring the new gear but the old gear wasn’t to hand when we went to collect the new one. I do hope this doesn’t mean it was thrown away.

[Alan MellorParticipant @alanmellor68824]

Screw to a square of ply and hold in the 4 jaw?

Alan

[JasonBModerator @jasonb]

Clamp the big gear to the faceplate, set hole to run true and bore. If it were me then I would use my softjaws.

[Brian RutherfordParticipant @brianrutherford79058]

I have seen various threads on these milling machine plastic gears where the operator has been blamed for taking excessive cuts thus stripping the teeth. I have had a toolco 32 (same as warco wm18)  from new. The first one went in the first 12 months. Very surprised as I had not been taking heavy cuts. Second one lasted 7 months again still not using heavy loads. Then it dawned on me what the cause was. Heat generated in the spindle was softening the gears. Fitted a 100mm computer fan into the casing above the motor to cool motor and spindle and never had a problem in the next five years.

 

[Brian Rutherford]

On Brian Rutherford Said:

Fitted a 100mm computer fan into the casing above the motor to cool motor and spindle…

That is a good idea.

With tongue in cheek, I have to say that all the high end computer people these days use water-cooled CPUs.

For the 3DP gear, maybe he can put a rotary union on the mill spindle and drill a couple of holes in the gear. The voids in the infill would allow internal coolant circulation.

[JasonBModerator @jasonb]

The MJF prints are usually solid so no voids

[JasonB]

On JasonB Said:

The MJF prints are usually solid so no voids

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On DC31k Said:

On Brian Rutherford Said:

Fitted a 100mm computer fan into the casing above the motor to cool motor and spindle…

That is a good idea.

With tongue in cheek, I have to say that all the high end computer people these days use water-cooled CPUs.

For the 3DP gear,

Not a CPU Fan, a 100mm case/ enclosure fan. Very quiet low power. 240 volt.

 

 

[Bill PhinnParticipant @billphinn90025]

Thanks a lot for the further contributions.

I don’t remember my gearbox ever getting warm, but I’ll watch out for that in future.

One thing I don’t have for my lathe is a face plate.

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