Gear material (Changewheels)

[grim_d]

Hi all,

I have nearly collected everything I need to make the metric conversion changewheels for my lathe, I've got the mill, universal dividing head, big enough micrometers, gear cutters...the list goes on.

I'm looking for thoughts on my choice of material for the gears, the machine in question is a Harrison L5A, it has metric dials but an imperial lead screw, I know the standard response is "use anything you can get a hold of" but I'm looking to permenantly convert it to metric with the changewheels so I would like to do it only once if possible, particularly the 127T gear, In this case because I have the norton gear box I need an extra 40T, 63T and 127T, I can keep the 50T gear already on the top shaft.

The 40T and 63T gears are for the intermediate shaft, I was going to use Acetal POM C as it's fairly cheap and machines easily, tufnol might have been the ideal but it comes with additional minor machining challenges and its horrible and dusty, I think the Acetal will do just fine, I can remake these If they get damaged.

The 127T gear has a diameter of about 9.25" and a thickness of 7/8" so a slug of material is proving quite hard to come across, the only thing I have found that is big enough is someone selling custom plasma cut discs of 20mm S275 steel, ordinary mild steel, not particularly cheap at about £40. Now i'm sure this will work just fine, even if it doesn't machine that great or leave a great finish. But I wonder if there's a better option? A chuck of cast iron would be nice. I don't have anywhere near me that I know of that I can go and beg an offcut from.

Thoughts?

G

[CCWKen]

It can be hard on tooling but the old iron barbell weights make good stock. Some claim it's dirty with foreign material (slag), un-melted scrap and such but the one I used was just hard. It machined ok but it was like an old iron pot--Hard as heck.

[Bob Engelhardt]

I made a couple of change gears out of aluminum. My principle reason was that if a gear is going to break, I'd rather it was one of these. I can re-make one of these much more easily than any other one. I have the material AND the right cutter. In normal use, the aluminum will last way longer than I will.

For your huge gear, you could cast a blank in aluminum.

Bob

[grim_d]

It can be hard on tooling but the old iron barbell weights make good stock. Some claim it's dirty with foreign material (slag), un-melted scrap and such but the one I used was just hard. It machined ok but it was like an old iron pot--Hard as heck.

Thought about that, trouble is big enough ones would cost as much as the bit of steel plate. Plus the bore is too big, extra machining and id rather not chew my cutter up too badly, I don't have the facilities to sharpen them.

I made a couple of change gears out of aluminum. My principle reason was that if a gear is going to break, I'd rather it was one of these. I can re-make one of these much more easily than any other one. I have the material AND the right cutter. In normal use, the aluminum will last way longer than I will.

For your huge gear, you could cast a blank in aluminum.

Bob

I suppose that is an option, it's another extra cost to set up for that thought I have been stockpiling alu for that very reason. Just haven't got round to building a foundry.

If I can find a way to get some melted I will have a go at that.

[CCWKen]

That would be the way to go. A few bricks or a sack of concrete, propane torch and something to melt the aluminum in is all you need for a one-off. No need to get fancy and build a foundry. Pour it into a leveled open oil sand mold.

[mattthemuppet]

I don't know how much your lathe can swing (I'm guessing 10in?) but a shadetree option is to rough cut a disk out of a piece of plate, drill a hole in the center big enough to bolt it to an arbor you can hold in your chuck, then turn the outside round and to diameter. I've done that for a couple of chuck backplates and it works fine. Tedious and time consuming, but cheap!

[MattiJ]

I don't know how much your lathe can swing (I'm guessing 10in?) but a shadetree option is to rough cut a disk out of a piece of plate, drill a hole in the center big enough to bolt it to an arbor you can hold in your chuck, then turn the outside round and to diameter. I've done that for a couple of chuck backplates and it works fine. Tedious and time consuming, but cheap!

And if you are adventurous enough you can trepanning cut the plate in lathe.
Like this:
http://imgur.com/a/gpcK9

Compared to normal parting tool the difficulty level is "something else" and you might end up like this:
https://en.wikipedia.org/wiki/Trepanning

[old mart]

Aluminium would be better than steel to practice on, or even Delrin sheet of the required thickness which is self lubricating and quiet.

[Andre3127]

What is the bore size and width of the gears you need? Can you calculate DP?
I might have a gear set I can mail you. PM me more info if you're interested. They came with my lathe that has a QCGB so they're of no use.

Sent from my XT1053 using Tapatalk

[Peter.]

For the 40 you could buy an old 45 tooth gear from G&M for £10, turn the teeth off and the diameter down for your lower tooth count. The radius difference between the two is 0.175" but the teeth are only 0.154" deep so it'll work out perfect. You could try the same thing using the 72 tooth to cut your 63 but you would have to remove .321" off the radius which might leave you tight for cutting new teeth.

http://www.gandmtools.co.uk/product-...pares-tooling/

[enginuity]

I know I'm suggesting a completely different path but you can 3D print using Acetal. I would serious consider this for change gears. I think you would find they will hold up fairly well.

[grim_d]

That would be the way to go. A few bricks or a sack of concrete, propane torch and something to melt the aluminum in is all you need for a one-off. No need to get fancy and build a foundry. Pour it into a leveled open oil sand mold.

I was thinking even more gash with some charcoal and a hairdryer!

What is the bore size and width of the gears you need? Can you calculate DP?
I might have a gear set I can mail you. PM me more info if you're interested. They came with my lathe that has a QCGB so they're of no use.

Sent from my XT1053 using Tapatalk

14DP, 14.5Pa, 7/8 bore, 1/4 keyway, 3/4 width.

I imagine postage would be a killer. Plus I've invested in all this equipment now so I should use it! Thanks for the thought though

For the 40 you could buy an old 45 tooth gear from G&M for £10, turn the teeth off and the diameter down for your lower tooth count. The radius difference between the two is 0.175" but the teeth are only 0.154" deep so it'll work out perfect. You could try the same thing using the 72 tooth to cut your 63 but you would have to remove .321" off the radius which might leave you tight for cutting new teeth.

http://www.gandmtools.co.uk/product-...pares-tooling/

I going to stick with the acetal for the intermediate gears. Should be plenty strong, less wear and works out less than £7 per gear.

I know I'm suggesting a completely different path but you can 3D print using Acetal. I would serious consider this for change gears. I think you would find they will hold up fairly well.

Tried it! My friend has a small, cheap 3d printer, tried to make a 127t gear using PLA that fit over my 100t gear. Had too many problems with the part lifting during printing. Bought the dividing head now.

[elf]

Acetel (POM) will off-gas formaldehyde which is not exactly healthy to breath If you do 3d print with it, make sure it's well ventilated. I've had good success printing nylon gears for low power applications. Printing a set of change gears for my Logan is in the planning stage, so I can't say how well they will work. Cost per gear should be around 50 cents.

[Bob Engelhardt]

... A few bricks or a sack of concrete, propane torch and something to melt the aluminum in is all you need for a one-off. ...

9.25 diam x 7/8 is quite a bit of aluminum - a 4" crucible almost 5" deep. I'm not saying a few bricks and a propane torch won't work, but it will likely be pretty frustrating. More heat would be better - a weed burner or multiple torches.

[grim_d]

9.25 diam x 7/8 is quite a bit of aluminum - a 4" crucible almost 5" deep. I'm not saying a few bricks and a propane torch won't work, but it will likely be pretty frustrating. More heat would be better - a weed burner or multiple torches.

Looking at it more I might aswell go the whole hog if im going to melt aluminium.

I've been looking at jet burners for foundrys and the like, easy to machine, might even have enough scrap kicking around. Ive got an old butane bottle I always intended to use to make a foundry

Basically just need some refractory and a regulator.