a little dentistry

[Bertie_Bassett]

finally had the time and the inclination to do a bit of repair work to my poor little lathe. unfortunately the first job was taking it to the dentist!

this poor lathe was badly abused in a past life and really needs a full refurb but that will have to wait. for now its just a case of fixing little bits here and there in the attempt of making some improvements.

anyway onto the job at hand!

when i picked up the lathe it had only a couple of its change gears and one of them was missing a tooth, iv put up with it for a few years, as there is a tiny stub of tooth left to drive things, but i had a bit of time so thought id get it done.


initially plan was to remove the offending stub, to braze some steel pins in and file to fit, but for some i didnt want to have to heat the whole gear up so i went for a different approach

first the gear was mounted in the mill for the extraction. A 2mm end mill took out the base of the broken tooth and provided a slot for the new one to sit in. The root was drilled out with a 2mm bit.

I also opted to leave the stub of tooth in place, it would have been a lot simpler to remove the entire tooth but i thought it might give some extra strength. and give me a guide to follow for filing the shape.

next step was to find somthing tooth shaped to make a new one out of, i dont have any cast iron and didnt really want a hard steel tooth to potentially damage the others so a bit of 2mm thick brass was cut to shape and filed to give a reasonble fit.

everything was given a clean up and soak in degreaser while i went looking for my jb weld, unfortunatly the elves must had hidden that as it was nowhere to be found. 
not wanting to give up i thought about plan A and brazing things but that would likly melt the brass tooth leaving me with a mess    so instead i thought id silver solder it in place.

a bit of flux was applied to the mating faces and the new tooth was tapped into position, then out came the propane torch 

after quite a bit of heating, ( cold workshop and no hearth ) i finnaly got the gear up to temp and managed to get some solder to run. whether or not its actually penetrated im not sure but the new tooth seems to be firm.

a bit of work with a file and the new tooth looks about right, iv given it a quick run in the gear train and it seems to mesh without any tight spots or odd noises o ill call it a success for now.
Time will tell if it holds in place, chances are it will be fine until im halfway through cutting a thread on a nearly finished part.

[b.lindsey]

Nicely done Bertie. It has to be better than that broken tooth.

Bill

[Kim]

That does look like a pretty nice dental crown there! 
You should consider open your own practice!
Kim

[crueby]

That does look like a pretty nice dental crown there! 
You should consider open your own practice!
Kim

I thought about doing that once, but it is SO hard to get the patient to put his head in the mill vise!   

Great work on the gear!

[Bertie_Bassett]

thanks guys, hopefully it will hold in there without rotting out.

seems to run smooth enough, i would give it a hard run with some thread cutting but i need to delve deeper into the headstock to check the shear pin for the gear dive, its going round ok, but something appears to be loose internally.

[ShopShoe]

Good Job.

I've seen YouTube videos of similar repairs to large gears for larger machines done almost exactly the same way. I think this repair will serve you well for quite a long period of time.

I like the idea of keeping things running yourself rather than what our throwaway society expects nowadays.

Thank You for posting,

ShopShoe

[Bertie_Bassett]

continuing on with the theme of teeth, i thought i would make a start on making a few gears to replace some of the change gears that are missing.

my lathe is a Denford viceroy which has 20PA 18DP gears, i cant seem to find reasonably priced involute cutters for these and as i need nearly all of them buying new is an expensive option.

i did consider making my own involute cutters using the button method but in the end settled for a rack type cutter as it seemed simpler and should cut any gear i want with only the one cutter.

first thing to do was to make the cutter, this involved quite a bit of maths to work out the correct rack dimensions but once that was figured out it was just a simple turning job. - unfortunately i seem to be missing some photos  hopefully the rest will make sense.

next step was over to the mill to turn the round profile into something with some more bite! so out came my new (bought a year ago but not unboxed) rotary table and in no time at all 5 cuts were made.



now the next step should be to harden and temper. . but im impatient and being as im only cutting delrin i decided to press on and see what it would do.

so some blanks were turned up to the right diameter for 16T, 20T and 24T gears and a 9/16ths hole bored through before parting each off to the correct thickness


next they were mounted on a mandrel  and the teeth cutting began!


after a lot of handle turning and counting of holes on the dividing plate out came a finished gear !


a bit of cleanup to remove the burrs and here the 16T gear installed on the lathe





and here's a couple of them up against an original cast iron gear.



fit seems to be reasonable, the tooth flanks are made up of a couple of flats rather then an actual curve, but for this purpose they should work fine.

next time i may try to double the number of flats per tooth to approximate the curve better, especially as the next ones will probably be a harder material.

[Ramon Wilson]

HI Bertie - that's a nice reclamation on the gear tooth  which should see you ok for quite a while.

It'll be interesting to see how those delrin gears hold up too 

Good to see you're finding some time in the workshop - hope it's not too cold

Tug