Hostaform, Nylon or Steel For Mini Mill Gear?

Had a happy day yesterday making my first ever foray into milling with my new to me but rather second hand Axminster mini mill. I had nearly finished making some t nuts when a things suddenly stopped turning. I soon diagnosed the problem as stripped teeth on the plastic spur gear between the motor and gearbox. I phoned Axminster this morning and am waiting to hear from them but don't have much hope they will have the spare so I've been looking elsewhere and seems there are plenty of cheap alternatives out there but which material to go for? Tempting to stick in a steel one but I imagine this gear is a designed weakpoint to protect the gearbox. Delrin I have heard of but I can't find the exact one I want but there are lots selling Hostaform and Nylon 6. Any advice on which material is best would be appreciated.

Thanks, William.

This article might be a useful starter.

Thanks David, I saw that one and it seems to suggest that Delrin is the strongest but maybe someone has tried the Hostaform in a similar application and can tell me wether it is up to the job. Or else maybe someone could recommend a suppplier for Delrin gears. I need a 30 toothe Mod 1,5. Needs to end up 10mm thick plus a 3mm boss, 10mm bore and a 4mm keyway but I suppose I can machine to all those dims on the lathe if it starts oversize.

William.

Folks who wonder if nylon gears in mini-mill and mini-lathe headstock might be interested to know this is a feature shared with the Denford Synchro.

Neil

William,

If you look at Arc Eurotrade web site you might just find a picture of a mill very similar to yours and if you look at the parts list you may well find they have exactly what you need sat on their shelf which for less time and probably less money they could send you, over you making your own.

Paul.

Delrin & Hostaform are brand names for FAMILIES of resin. Within each there may be many different grades with tailored properties.

The article compares homopolymer actetal, vs copolymer acetal (without details of composition) vs Nylon 6. Plastics rapidly become fiendishly complex, even within a family. Don't expect a simple answer.

The original Denford gears were made form a material called Technyl A90, whatever that is, probably a nylon as the name suggests. I have made quite a few replacements from Delrin.

The original Denford gears were made form a material called Technyl A90, whatever that is, probably a nylon as the name suggests. I have made quite a few replacements from Delrin.

I found that the original gear was rather mis-shapen on my lathe and it used to bind after it was worked hard and the heat caused it to swell. The delrin replacement never suffered any of this.

William, I have an Axminster MiniMill and when I bust my gear, easy done, I bought a replacement from ArcEurotrade, can’t remember how cheap it was but they are brilliant at responding to orders, I think it was here the day after I ordered. If you go on Arc’s website they have a comprehensive parts list for the minimill and ordering couldn’t be simpler. At least you can get running again until you decide what or which material you will replace it with.

Dave W

Thanks Dave, found it., ordered it. I noticed they also do steel replacements for the high low gearbox gears, have you fitted those? I wasn't planning to make a replacement for this although ironically I bought the mill with a view to making metric-imperial conversion gears for my lathe.

William.

William,

Unless you really need want them, it is better to stick with the nylon gears - which act at a fail safe. Also, the high/low gears are cast iron. They will make your lathe more noisy. There are users who still want them, so we sell them for the old geared C2/C3 metalworker mini-lathes. If you still want them, consider the bigger one to be metal and the smaller one to be nylon which may still build in a small amount of fail safe.... although I am aware that this combination suggestion is questionable with certain people.... but it also works.

Ketan at ARC.

I have always reckoned that gears should be unbreakable not fail safe and that plastic of any sort for this job is used because it is far cheaper to injection mould a plastic gear than to machine a steel one. A sheer pin device would be used if protection was considered necessary but I have known a Tufnol gear to be used in a gear train to reduce noise. If my minimill gears ever strip I shall replace them with steel/cast iron ones and grease them well. Colin.

I understand Colin,... in which case... probability of electronics - board giving up the smoke can increase, and we are happy to sell more expensive components such as control boards...

Ketan at ARC.

William, I stuck with plastic gears for the reason that Ketan illustrated, better to replace a sheared plastic gear than an expensive burnt out electrical board. I don’t use my minimill that frequently because I now have a Champion V20 mill which I have fitted with DRO’s and other mods, giving me much more machining capacity. Glad I was able to help solve your issue.

Dave W

Does the control board have no overcurrent / overload protection then? Just a question . Colin

Depends on the machine. The lowest spec. mini-lathes don't have. Also, on such mini-lathes, and even on high/low geared mini-lathes which have an overload protection, there is a 'user' element to be taken into consideration. If a new user, then failure - damage is related to how the stoppage occurred - heavy handed due to incorrect/improper/inexperience use?... in which case, probability of gear breakage (nylon) or board failure or both, could be equal. If metal gears + entry level electronics + new inexperienced user, then board failure event probabilities increase. There is no clear reason. Just probabilities related to user.

Ketan at ARC.

Thank you Ketan for that information. Colin