Mr Pete – Loading the gear train

[not done it yetParticipant @notdoneityet]

Which loads the gear train more?

A recent u-toob video by the above has demonstrated making 3D plastic gears and then ‘tested’ one. I reckon increasing the feed rate would stress the gear train more than increasing the depth of cut, but he, and a couple hundred others, reckon increasing the depth of cut with constant feed rate is a fair test for testing a plastic gear in the train.

What do you think?

Edited By not done it yet on 13/01/2018 18:57:46

[not done it yetParticipant @notdoneityet]

Does depth of cut or feed rate increas the load?

[HOWARDTParticipant @howardt]

Power calculations take both into consideration. So increasing either has the same effect.

[not done it yetParticipant @notdoneityet]

HowardT,

He was not actually assessing the machine power, just the durability of a plastic gear in the long/cross travel gear train. His aim was to demonstrate the plastic gear at differing loading. I think depth of cut affects the motor loading and feed rate (at constant depth of cut) affects the gear train loading. Him only changing the depth of cut, I believe, was not a fair test of loading the gear train.

[JasonBModerator @jasonb]

Both will increase the amount of metal removed per rev so as Howardt says if you double the feed rate that is equal to doubling the depth of cut

[HOWARDTParticipant @howardt]

There are two calculations one for wear and one for strength. If I remember it right I always did the strength and only the wear sometimes. The strength was allways less than the wear, at least in what I was doing, working with constantly lubricated gears.

[HOWARDTParticipant @howardt]

Having now look but not listened to his video, he is looking at using 3D printed gears for his Atlas lathe. Very different to a cut gear. I will listen tomorrow to get exactly what he is trying to achieve.

[Mark RandParticipant @markrand96270]

I would suspect that the variation of load on the carriage drive with increasing depth of cut would depend to a great extent on whether a positive rake or negative rake tool were used. High positive rake, little or no variation. Negative rake, great variation.

[HopperParticipant @hopper]

Having used the leadscrew handwheel on my old Drummond Flagellator to manually feed the carriage for many years, I would say that both increased depth of cut and increased feed rate cause an increase in the amount of force needed on the leadscrew handwheel. Purely subjective of course, but that's my experience.

[Carl Wilson 4Participant @carlwilson4]

This is very interesting. My friend Richard and I have been making 3d printed change gears for about 18 months now. We are using a Formlabs SLA machine and the resins we use are the tough types made by Formlabs. Unlike plastic filament or recycled PET bottles etc, these are engineered materials with empirically derived published mechanical properties.

When we made the original set for my Harrison M250, we decided to test them by progressively increasing depth of cut and feed rate together on my machine. This was done on a 50mm piece of 316 stainless steel round bar.

We saw increasing both variables as a quick and dirty means if progressively and rapidly loading up the gears. Even with very heavy cuts and feed rates on the 316 the 3d printed Gears showed no signs of strain or wear, either on the teeth or driving features.

[not done it yetParticipant @notdoneityet]

All I am saying is that doubling the feed rate at constant depth of cut is going to increase the gear train loading more than doubling the depth of cut at a constant ( small) feed rate. If one wants to test the plastic gear, one needs to at least show the effects (if any) of loading that gear and not by just increasing depth of cut.

Work done in moving the carriage horizontally will be reflected in the loading on the gear train. Same amount of material removed could be half the cut and twice the feed. That would load the gear train! Not the way it was done on the vid.

[Neil WyattModerator @neilwyatt]

Increasing the feedrate means changing the gears, which means you aren't doing a consistent test.

Increasing DOC increases the load on the same gears, a fairer test.

Neil

[Carl Wilson 4Participant @carlwilson4]

Increasing the feed rate means changing the gears..depends on the lathe I guess. Not in our case.

[HOWARDTParticipant @howardt]

Having watched the video. this time with sound, he was testing a solid printed gear made from PLA. Yes he increased the feed using the variable feed box and the gear was in the train between the spindle and the lead screw feed box. He increased the feed rate a couple of times but at the end remained on the same feed rate but increased the depth to create a stall/belt slip. He showed that the solid PLA gear will transmit the required horse power at constant load. What still is required is a wear test, time running and shock load. Having said that it showed that PLA gears on some lathes may be a suitable substitute for expensive originals if you have a 3D printer.

[HopperParticipant @hopper]

That's really interesting. Considering the faffing about with dividing heads and the expense of a set of eight special gear cutters required to make a set of change gears (or much more faffing about to make your own cutters) 3D printers may provide the way of the future, now. Certainly would make building your own QC gearbox more cost-effective if you didn't have to purchase 20-odd conventional Myford gears to do the job.

[Carl Wilson 4Participant @carlwilson4]

I’ve watched it too. My own experience with the tests that we did on our production 3d printed Gears showed that even under heavy stress at the cutting tool they are still relatively lightly loaded. There is still a feedshaft/leadscrew gearbox between the change wheels and the “load”. The ones we made were and are just as good as the phenolic gears originally made by Harrison themselves.

At the end of the day it is a difficult test to make. You’d have to run them loaded for thousands of hours to check wear etc. Making chips at different feed rates and or depths of cut isn’t a practical way to do that.

We concluded that the gears that we made at least would last many years given that they are relatively lightly loaded in most cases and are often rarely used. That said the mechanical properties of the material suggests long term testing would also result in a positive outcome.

[Russell EberhardtParticipant @russelleberhardt48058]

Interesting tests although I was a little surprised that his 12" lathe overloaded at those depths of cut. My 10" Atlas copes with that O.K.

I note that the printed gears are 20° pressure angle while the original Atlas gears are 14.5°. I'm no gear expert but wonder what effect running mismatching gear would have.

I have a full set of change gears but might have a go at printing a couple to reduce the noise when set up for fine feed.

Russell

[not done it yetParticipant @notdoneityet]

Posted by Russell Eberhardt on 14/01/2018 14:48:09:

… to reduce the noise when set up for fine feed.

Russell

Do I take it, from that statement, your gears rattle when not under much load? Kinda means that extra feed, rather than depth of cut, loads up the gear train?

Exactly my point.

[Russell EberhardtParticipant @russelleberhardt48058]

Posted by not done it yet on 14/01/2018 15:26:43:

Do I take it, from that statement, your gears rattle when not under much load? Kinda means that extra feed, rather than depth of cut, loads up the gear train?

Exactly my point.

The feed gear train rattles when not under load. It is somewhat quieter when the feed is engaged at the saddle and the cut is proceeding.  I set the gear spacing using a bit of printer paper between the ZAMAC gears to give some running clearance.

I don't see how that proves that the feed rate rather than depth of cut. I suspect that both will affect it, how much each will affect it is likely to depend on many factors including the geometry and sharpness of the tool.

Russell

Edited By Russell Eberhardt on 14/01/2018 15:45:05

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