TOPIC:

eddrick wrote:

It'll be interesting to see what they go for, there can't be many good sets left

They're both on a "buy it now" basis - I'm surprised they haven't gone already TBH, especially the clean set

Bit of an update ...

Scorcher spool & 45T spur heavily machined down (originals on the right):




... resulting in a lot of shavings





Bits stuck together with Araldite...








Spacers made up & fitted along with new spool - note that teeth on the large side are considerably narrower than the (original) A & B gears here...






...

Making new A & B gears, small gears (15T) didn't need any machining initially, large side (35T) needed a couple of mm taking off the boss (left & centre ones have been done here):





Drilling out centres...







New A & B gears fitted, spacers still need making.

This is where it started going wrong - thanks to various inaccuracies in alignment of the gears & the centre drilling, and only having a 4mm drill bit to fit the gears on a 4mm shaft (actually 3.95 vs 4.05, and therefore a bit of binding), using any two out of the 3 "new" gears (& one original) was fine, using all 3 resulted in the gears locking up & the Araldite joints failing

I have some 4.1mm & 4.2mm drill bits to add in a bit more tolerance, but I also need to find something that will stick the Delrin gears.

Awesome bit of equipment there, Jonny.
JB Weld might work better than Araltide?

Wow! What's this? A hobby-turning machine? Can you use it also for alloy?

Unimat arrived then! How are you getting on with it? - looks to be going well!
Did you solve the tailstock chuck requirement? - Proops are doing Chinese 0-6mm chucks with 1-Morse taper adaptor for about 6 quid at the mo - how is the collet chuck fitted to the Unimat tailstock?
Have you tried it with metal yet?

Gear part interfaces -
You can't glue delrin, but it's weldable.
OR drill & pin the 2x parts at the interface diameter (Or drill, tap, grubscrew & locktite).
Best aim for an interference-fit between the parts, so they have to be forced together in the first place - say 0.05-0.1 undersize bore, 0-0.05 oversize spigot (Delrin has got lots of "give" & "creeps", so you need comedy interference). You might get away with more interference if you stick the spigot in the freezer & the bore somewhere warm before pressing together (Use the tailstock to ram one part into the other part mounted in the chuck).

Shaft clearance - if the shaft is 4.00 O/D, a 4.00 drill will work well if you get the spindle speed up & "work" the drill back & forth through the hole a few times (Try it occasionally, so you don't overdo it). Plastics have a habit of their holes shrinking after drilling - some of the material gets cut, some "gets out of the way" of the bit then returns to shape after. Don't be tempted to drill with a bigger drill as it will remove too much

Just thought of another idea for joining the gear bits - friction welding
Make the bits a light interference fit (ie, you can still just spin one inside the other by hand), then mount the assembly in the main chuck & grab hold of the inner gear with the tailstock chuck. Fire the machine up briefly then stop it. Hopefully, the friction of one part spinning within the other will melt the delrin & weld the parts together.
Try that....

eddrick wrote:

...

I can't remember the dimensions, but the outside of the inside gear is significantly bigger than the inside of the outer gear, I also tried rigding the mating surfaces on a couple of them with a scalpel before fitting, hoping that would reduced the chances of them spinning...

I've looked up adhesives suitable for Delrin, I gave up after the 3 I looked at all turned out to be epoxies - I relly need something that going to do a bit of melting...

Pinning is just not an option, there's not enough room

I was intrigued by the possibility of friction welding (I remember seeing that demonstrated at TWI 20 years or so ago), so I gave it a go, 10 seconds spin on one, 15 on the other ... it's looking promising so far



Tailstock thread is M12 x 1mm ... I haven't tried it on anything vaguely metallic yet & not sure I ever will - this is a monkey copy, remember, not the pukka Unimat. I at least need to get the tool holder sorted a lot better first.

I've fitted one of the new gears to the Holiday buggy with a broken tooth ... the first one was so out of round it bound the gearbox up so badly I was worried it would shred the spool in use but the 2nd was a lot better.

I've also fitted a TBG gearbox cover to it... without any instructions or examples of how to fit it I had to guess how it went on but it's probably marginally better than not having it The holes will get covered up before I test drive it, that'll have to wait for the time being.

I aslo fitted one of the TBG covers on a 380 equipped Sand Rover ... it's clearly not designed for that setup, but seemed to work out ok

I might have a M12x1 tap, failing that screwcutting any size is possible on the lathe. When you get a chance, post (Or send me) a pic of the tailstock assembly "exploded" so I can see what the story is, & maybe come up with an adaptor to use more standard equipment with it (ie morse taper).

Option 3 for joining gears - is there any feasiblity for making the headstock chuck indexed, or at least some form of degree-marked plate? - you could cut "splines" on the parts using the carriage/tool to chisel out the material, with the chuck stationary at a required angular setting (eg a spline say every 5 degrees).
Too small for pinning? Pussy...

A tip fo machining gears, particularly those with non-divisible-by-3 quantities of teeth - chuck on a lump of bar/tube & machine a bore that will only just pass the O/D of the gear. You need to end up with a really thin-walled tube, so that when you tighten the chuck, the tube grips the gear. Should have things running much more true.

I would've thought the machine would be ok on ally at least, I'd be quite surprised if it wasn't