Gear Material Help

[chiliviking]

I had a crash today with my Sheldon lathe and it ate the teeth off the gear in the reverser/lead screw drive assy. The gear was phenolic so it sheared the teeth without further damage. I called National Acme ( dealer for Sheldon parts) and was told the gear was not in stock but was available. I asked how much and was told $595 and it would take 4 to 6 weeks. When I regained conciuosness I said thank you , have a nice day. He was insulted that I thought that was a rediculous price.

I ordered an involute gear cutter from MSC and will make my own. I now need to decide on a material that will have properties similar to the original phenolic. If this happens again I want the gear to shear rather than tear up the whole gear train. If using a plastic material of some kind I will press a brass bushing in the center. The gear is engaged any time the lead screw is turning so wear is a factor.

What suggestions to you all have?

 

[cfellows]

Have you checked on eBay for phenolic? I see it out there in sheets now and again. What are the dimensions and pitch of the gear?

Chuck

 

[chiliviking]

The gear is 2" dia., 16DP, 30 teeth, a little over 5/8" width, 9/16 center hole.

 

[tattoomike68]

NYLATRON
http://www.gcip.co.uk/EP/materials/nylatron.htm

We have used it for gears that run the governers for hydroelectic turbines at the dams here in the northwest. its good stuff.

 

[BobWarfield]

Chili, sorry to hear about the price for that gear. Sounds like they charge that much because they can, more than because it's worth it.

I've wanted to make some gears but haven't yet had a good excuse. Please do give us some photos and a bit of blow-by-blow?

I know there are lots of folks making leadscrew nuts out of Delrin. Don't know if that makes it a good gear material or not though.

Best,

BW

 

[AllThumbs]

Choice one: Delrin.
Choice two: PVC
Choice three: UHMW

In that order

 

[Powder keg]

I redid 4 gears in my LeBlond's headstock a few months ago. For the main bad gear they wanted $1200. It wasn't to bad making my own. You can do it.

Wes

 

[Rog02]

Have you checked on eBay for phenolic? I see it out there in sheets now and again. What are the dimensions and pitch of the gear?

Chuck

Phenolic is usually available from any of the places selling homebuilt aircraft supply stuff as it is still used as push rod bearing surfaces where the push/pull rods pass through bulkheads.

 

[compound driver 2]

Hi
Never machined Phenolic but I do have a memory that its not too good for you in dust form. Dont quote me but could be worth a mask during milling.

Cheers Kevin

 

[Circlip]

For preference I would be inclined to use Phenolic as per the original, my Maximat has a main spindle compound pair made from Phenolic and in a previous life, some numb nuts managed to partially strip the sides off some teeth by not engaging the speedchange properly. Looking at the prices you are having quoted over there it would mean selling the car to buy a replacement. I would have thought that when the Sheldon was originally made that plastics were available to use for this gear, so if they were, why didn't they use them? I would also think that the gears used in the drive trains of lathes would be molded rather than cut, - tooth strength. The Phenolic materials used over on this side of the pond had the trade name TUFNOL and available in different grades and while the Nylon type materials would do the job, I would think that in practice the position of the gear would make the teeth "Spread" in service. In the event of another lock up, what would give first? PS. If you do use phenolic, a.Cut it from sheet, not bar.
b. Make a spare at the same time.
Best regards Ian.

Only a personal opinion, no offense to any of the posters working in the trade.

 

[kellswaterri]

Hello all,
if considering the use of ''TUFNOL''.. please bear this in mind...recently I had a P/M on another Forum from an individual with regard to a post relating to the use of ''TUFNOL'' he wanted to know whether it could be proven that it could contain ''ASBESTOS''...Now I am not a legal eagle ...but he might well may be... so I directed him to do some further Research on the subject...FOLLOWING my own advice and more hunting on the net I would strongly suggest not to use it...WITHOUT FULL FACE MASK protection.
All the best for now,
John.

 

[paulj84003]

Have you givin any thought to making the gear out of aluminum, using a very narrow face on the teeth. and or making an alum gear attaching it with a shear pin.

 

[gilessim]

As far as I know, Tufnol, was just cotton cloth soaked in phenol formaldehyde resin, and pressed or rolled, sort of a precursor to fiberglass ,printed circuit boards were (maybe some still are!) made from it, there were also paper and other fiber and phenol based products, Bakelite is another, it could well be that aspestos was used aswell but anyway phenolic resins are very brittle and have no "give" I would go for Delrin or PTFE, I had a helical gear made by a friend for my mig welder a few years ago after the original one broke in 10 months (that looked like PVC) he made it from PTFE and its still going strong!

Giles

 

[rake60]

I have cut rather large parts of phenolic, Including a few 4 foot dia gear blanks.
I can tell you first hand that it's not pleasant stuff to work with, even with an
industrial dust sucker placed 6 inches away from the cutting point.
For a few days after cutting it, you feel like you'd been crawling around in the
attic insulation.

It cuts like chalk but requires very sharp tooling. If the tooling is anything less than
sharp you'll end up with something resembling a sheep dog.

A good dust mask is a must on any scale!

The phenolic material that would be used for a gear would be a cotton or canvas
cloth base material and phenolic resin. There are also materials that use a glass
cloth (fiber glass) instead of cotton. The glass makes it even more entertaining...

The resin polymer it's self is made from Phenol and Formaldehyde.
Give those elements a Google search.

As with anything else, it can be machined safely, as long as you understand the
required precautions.

Rick

 

[Circlip]

Over here in Brown's Fantasy land, we are constantly being bombarded by the "Nanny state" to tell us what not to do cos we might hurt ourselves. One or two things you should be aware of chiliviking. Don't machine the gear out of alluminium, sorry aluminum to you, the dust can cause Alzheimer's. Don't machine it from PTFE, the gas given off is poisonous. Don't let your wife buy pink coloured toilet paper, it could be carcinogenic. Don't operate your lathe/miller using electricity, a shock could kill you.
Thanks rake for pointing out some common sense. Some of the methods we use in our home workshops would never be allowed in industry, not because they are unsafe but if you take the lowest common denominator of a newbie operator who might injure themselves due to their inexperience, then you are making sure they get home with all their digits intact. Why can't you use the same cutting speeds for Aluminum/Steel/Brass? they're all METAL? I have my own opinion as to why Sheldon chose to make the gear from Phenolic in that application, but Hey Ho, you asked for other people's suggestions so YOU can choose, but don't be put off by other people's prejudices or fears. Rake has said it, make sure of all the factors and work accordingly AND SAFELY. Best regards, Ian

 

[rake60]

Good Points Ian!

Here in the USA caution is driven by attorneys.

Get a splinter in your tongue from an ice cream stick?
Just call their toll free number.
They'll track down the person planted that tree to see that you are
duly compensated for your pain, suffering, lost wages, mental anguish
and visible scars. :

It's the reason for the Disclaimer on this site.

EVERYTHING related to machining is dangerous.
Some have hazards that go beyond the normal dangers.
Safety comes FIRST. I would expect every member to point out
ANYTHING that they see as falling into that category.

Rick