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For the machinists amongst us!

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Shetland Biker:
not got a clue about laithes, apart from they make things round haha,  also not got the space, or the finance to buy one haha

Johnny4428:

--- Quote from: Orcade-Ian on April 13, 2024, 12:51:45 PM ---Just a quick note to tell you of a workaround.  I needed to reface a very badly pitted exhaust valve from a Fairbanks Morse stationary engine - 7/16" diameter.  I didn't want to use a 3 jaw as I knew it would chatter (slightly worn jaws) but only had a 12mm 5C collet.  Slid some heat shrink sleeving on the valve stem and warmed it up to shrink it.  Fitted the collet perfectly and produced a lovely finish on the valve seat face!  The heat shrink sleeving is so thin and the collet has so much radial contact that it was a very rigid set up.

I used to be an engineer but I'm OK now!

Ian
Beginning to realise how much you are asked and do for other people Ian! You’re a victim of your own talents. Thanks very much for machining my old rusty piece of junk! O’ and thanks for the tea, again!😜

--- End quote ---

McCabe-Thiele (Ted):
Another skill I never learnt not helped by not being allowed to do metalwork at school.

I've well and truly missed that boat now - thank goodness for the likes of Max who used to be a member.

AshimotoK0:
Nice one Ian,

I did a bit of that kind of thing during the 1st Covid  lock-down. I made a few adapters etc to have a go at machining down rubber rollers. My mate Graham Curtis found that on CB72/77 cam chain tensioners/idlers that the rubber appeared to be rock hard but if you remove a mm or so from the surface, the rubber underneath is still pliable. I have always shied away from using chemical softening as I reckon that may end in disaster if the roller breaks up after softening. Graham told me to use a very fast speed and really sharp cutting tool. This was a bit of a problem because I always get the guy at work to sharpen my machine tools (old school tool steel) but he was off work, being furloughed. I had a go at sharpening myself with limited success. He was correct that the underlying rubber was still pliable but I chickened out a bit as I was attempting rollers off a Black Bomber K0 cam chain tensioner assembly .... mega expensive unobtainium 2 rubber roller/one steel 'sprocket' affair.  Problem with the Bomber is that it  a very long and complicated cam-chain arrangement and I was concerned that removing 1mm or so from the diameter of the rollers might affect the geometry of everything. Then lock-down finished and I was back at work and moved onto other things. It's an interesting concept though. I wondered at the time if freezing the rubber would aid the machining. Graham has done dozens and dozens of the CB72/77 cam chain tensioners.

Has anyone else had a go at this. Only really worth it on 'unobtainium' parts though.

Orcade-Ian:
Ash, I did a similar although not as critical job as a Bomber on my Ajax bench grinder/tool sharpener.  It has a normal grinding wheel on the left and the motor shaft at the other end drives a series of rubber rollers to reduce the speed for a wet-stone for wood chisels and the like.  Quite heavy springs keep the rollers in contact and they end up with grooves and flats which prevent the white wheel from turning.  I was able to machine the damaged surface true again with a high positive rake on the HSS tool and top speed on the lathe (1000 rpm - wish it had more). As you say, the rubber was rock hard on the surface but just right underneath.

I also now use belt dressing on the rollers - but that's of no use in your application.

Ian

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