Very approximately, for steel, 100 deg. C differential gives 1 thou. per inch expansion difference. This seems achievable with domestic equipment but the crunch will be the need to mate the parts extremely quickly as the temperature difference will reduce rapidly as the items are slid together.

Edited By Clive Brown 1 on 17/07/2023 20:52:45

If this is any help.

When I made my Comparator, the 6.125" diameter x 1" thick, cast iron base was reamed 1", because that was the largest reamer available.

Having measured the resullting bore, the 1.125" column was turned down to be a thou bigger thann the bore.

The coumn spent the night in the freezer, so should have been at -18. The cast iron base was in the oven for two hours at Gas Mark 6.

The column was removed frrom the freezer and wrapped in a towel while the base was removed from the oven and placed on a piece of plywood on the kitchen floor.

The column was unwrapped, and instantly became covered in frost. It was a loose fit in the hot cast iron base. As time pssed the frost disappered up wards from the base.

Once evrything was at room temperature, the column was, and has remained, a tight, immovable, fit in the base

Which was the object of the exercise.

REcently did something similar with a a "plug" tdestined to fill a 26.5 mm hole in an embryo backplate for a 80 mm chuck. Timescales were shorter, so the pkug requiured some assistance to enter squarely intomn the bore, but withstood subsequent machining and boring and tapping 3/4 BSW. So the 0.001" interefernce fit must be sufficient.

Howard

Andrew,

If it is of any help and reassurance, in your earlier post I mentioned that I had seen a successful repair to a multipoint Britool socket with a sleeve over it to close a full length split.

My friend Richard who did that work was a time served engineer from Parsons Turbines and being a mean old sod he would have used whatever came to hand such as a piece of water pipe to make the sleeve! I don't suppose there was much sophistication put into the fitting job either, maybe some heat and a quick bashing together on an anvil top with a thick walled collar under a big hammer. I don't think for one moment he would put his mind to the degree of interference fit other than to bore a short lead into the collar that just fitted the socket and finish the rest of the bore to 1 thou under that.

Regards

Brian

I think the point was that the sleeve was split and this was a repair

As I understand it, this sleeve is intended to repair a Jacobs chuck with a split outer shell. In turn, the outer shell needs to be sufficiently tight on the internal split threaded actuating ring to prevent slip. I have had Jacobs chucks where these parts slipped when being fully tightened despite not being split! I doubt the repair will be successful unless the sleeve is substantial and a tight press fit.

Tried posting this a few minutes ago and it disappeared, apologies if it ends up doubled-up.

Just completed my first attempt at shrink fits, putting steel rims on cast iron wheel centres for a model loco. Wheel centres were 67mm dia, bored the rims to 0.1mm undersize, dropped the centres in the domestic freezer overnight, then this morning put the rims in the oven at 220°C for about 45 minutes, took them out and the centres just smoothly dropped in under their own weight, all except one . It is now stuck about 4mm from home with a slight misalignment. Don't want to press it the rest of the way as I don't have a press and doing it in the vice may put too much stress on the fairly delicate centres.

Thinking I could pop the assembly onto a loose fitting shaft, and rotate it slowly in front of the gas torch to see if I can heat the rim up enough to allow the centre to seat properly with some light pressure.

Any other suggestions?

Assuming mild steel rim on a cast iron wheel, there will be next to no differential expansion between them by heating. The stuck shrink fit parts will also be in sufficiently good thermal contact that they heat up in unison (unless you can attack the rim with a large jet oxyacetylene torch, which might just work if it doesn’t melt first).

There is really no alternative to resorting to press fitting to complete assembly. What this needs is tooling (parallel thickness spacers to directly support the offending parts, and a press or vice that ensures parallel and axial motion. With a sound setup there is a good prospect of successful recovery.