Gears

[Dick HParticipant @dickh]

Hi Gentlemen,

A question. A friend of mine has an old ice cream maker which has eaten a plastic gear, essentially a 47 toothed wheel with a concentric 11 toothed pinion, I estimate the module at 0.75. The machine has eaten some teeth off the pinion, game over. What sort of gear shape or form do such gears have? To me the teeth appear to have rounded tips and valleys and straight sides, else the tooth form is very triangular. Is there some particular tooth form used for plastic gears in electrical appliances? What is the correct term for such a gear, twin or double gear?

Regards,

Dick.

[Dick HParticipant @dickh]

A double gear

[Neil WyattModerator @neilwyatt]

Posted by Dick H on 25/07/2018 14:55:07:

Hi Gentlemen,

A question. A friend of mine has an old ice cream maker which has eaten a plastic gear, essentially a 47 toothed wheel with a concentric 11 toothed pinion, I estimate the module at 0.75. The machine has eaten some teeth off the pinion, game over. What sort of gear shape or form do such gears have? To me the teeth appear to have rounded tips and valleys and straight sides, else the tooth form is very triangular. Is there some particular tooth form used for plastic gears in electrical appliances? What is the correct term for such a gear, twin or double gear?

Regards,

Dick.

Such gears usually have a normal involute gear form, but the 11-tooth will probably have a modified form, although moulded gears can be made with undercuts not possible on cut gears.

0.8 mod gears are quite common, but in a bespoke application any size is possible.

Neil

[not done it yetParticipant @notdoneityet]

A pic might be helpful. Does it have a through shaft? What does it drive? Measuring the meshing gear may give you a better estimate of MOD or DP. Does it need a complete assembly or could a new pinion be fitted to the 47 tooth gear?

It might be a fairly common item or perhaps a candidate for 3-D printing?

What plastic? Could you grind a cutter to match the profile?

Can’t help, apart from making the suggestions for a replacement.

Edited By not done it yet on 25/07/2018 16:25:00

[Dick HParticipant @dickh]

Thanks for the suggestions.

From the dimensions I think 0.75 is OK for the mod. There doesn´t look like there is enough plastic there to put a new pinion in. I assume the original was either ABS or a nylon.

The whole thing sits on a 3mm shaft.

I found a 0.5 mod version of the arrangement in the web with a CAD file and scaled it to 0.75 and altered the vertical scale a bit. However my knowledge of CAD programs is minimal. Additionally I couldn´t get the slicer to give me a completely solid 3D print. My brush with 3D printing is in it´s early stages (just assembled a Geeetech Acrylic bags of bits) and I am on a steep learning curve. Still having fun to get things to stick to the bed. I don´t think PLA will have the mechanics for such a project. The wheel is 36.6 mm (47 teeth) across the points and the pinion (11 teeth) 10 mm.

It´s too hot to be outside (30+°C) so trying to find some gentle amusement.

I have set of 0.75 mod involute cutters and might try to make a version with a POM wheel and press fit Al or brass pinion. An alternative might be a 3D printed version with a brass insert. I don´t have the broken part to hand, only photos via email.

Given the simplicity of the tooth form, I probably could make a single or multipoint cutter. It just looked a bit of a simple tooth form.

Dick.

[Neil WyattModerator @neilwyatt]

Should be possible, I printed a PLA gear that provided a rescue repair for a school projector.

Do you have a heated bed? (On your 3D printer, we all have heated beds in the bedroom at the moment…)

Neil

[Dick HParticipant @dickh]

Many thanks for the input.

The 3D printer does have a heated bed which I run at 65°C for PLA. Perhaps I´m trying to many fronts at once. Any 3D printing tips welcome. At the moment I use a glue stick for adhesion.

Still not sure what settings to use in Slic3r to get solid prints.

Rather than pure 3D printing I´m much more interested in combining 3D printed bits and machined parts, It is still very early days.

Neil:- Thanks for the comment about the school projector, it works a bit slower. It just reminded me of running the technical side of a lecture at a congress some 30+ years ago when a Carousel projector decided to work like a pop up toaster, spitting out a whole magazine of slides. Anyway it shortened the discussion afterwards.

I have just automated a rotary table for cutting gears (according to Rex Swenson´s recipe).

[Neil WyattModerator @neilwyatt]

Ah! Dump the glue stick and buy some cheap washable PVA, dilute it 50/50 with water.

The reason I ask about heat is that nylon will print with a heated bed, but you may need a vey high bed temperature.

I use Cura. I find about 60% fill is effectively solid, but make sure your wall thickness is 3x nozzle diameter and you will get strong enough prints, even if hollow.

Neil

[Chris Evans 6Participant @chrisevans6]

Have a look at "Duval Gears" website or catalogue. You may be able to buy a couple of standard moulded gears and fix them together ?

Edited By Chris Evans 6 on 25/07/2018 22:36:52

[Howard LewisParticipant @howardlewis46836]

For anyone who is not able to 3D print gears, you could cut two gears, (Main Wheel and the Pinion with a extended hub) and then press / key / glue the Pinon into the Main Wheel.

I did this for both my ML7 and for a friend's ML4, in steel.

I found Davall Gears and some of the other companies offering ready made gears to be expensive

Howard

[fishy-steveParticipant @fishy-steve]

Hi Dick,

I did a similar repair for a work colleague a few months ago. He had stripped a plastic gear in his hedge trimmer.

Having measured the gears it became apparent that they were not of a standard form. The diameter and tooth count didn't match anything in the Machinist Handbook.

If you take a look in my album "gear cutters" you can see the modified gears. The gear the small pinion is bonded to had to match an existing drive pinion that was attached to the motor.

The two upper gears I made standard 1.5 MOD to match a fixed 40mm centre. You can see the difference in the standard MOD form against the non standard form of the lower gear.

Steve.

Edited By fishy-steve on 26/07/2018 13:36:12

[Dick HParticipant @dickh]

Many thanks all,

I think I have enough food for thought and will try a couple of approaches. I´m slightly grounded at the moment (don´t lift anything over 10 kg. etc. etc.) and this little project might keep me out of mischief for a while. That and trying to get my head round Fusion 360!

I´ll try to get back to you when I´ve had a go.

Dick.

[Author]

Posts