Machining cylinder castings from bar stock

[Peter Simpson 1Participant @petersimpson1]

At the present time I in the process of machining castings for my 5" gauge BR Standard Class 2.

I have machined the two blocks of cast iron to rectangular size, bored out the cylinder and valve chest holes to size. The blocks are now the correct three inches long with both ends machined parallel to the bores. The next job is to machine the external shape of the cylinder blocks. This requires the blocks to be rotated whilst milling the external radius.

I have seen this done by mounting the blocks between centers held on an expanding mandrel. As I do not have an expanding mandrel. What would be the best method to achieve this operation ?

[Peter Simpson 1Participant @petersimpson1]

[Thor 🇳🇴Participant @thor]

Hi Peter,

I mounted the cylinders on a mandrel when machining the cylinders for a 2-cylinder engine. I had made the top covers first and used them as jigs for spotting the holes in the cylinders. The mandrel I used had a flange with the holes on the same PCD as the cylinders. You can read what I did from page 6 here.

Thor

[not done it yetParticipant @notdoneityet]

I doubt that too many have expanding mandrels, at least not in multiple sizes. I often use mandrels and make them on the lathe as and when I need. Flange at one end and a suitable thread at the other. Bolted together with a nut and washer or screw and washer as befits the job.

Made in situ, when required, ensures perfect concentricity with the chuck. Yours are likely not in need of perfect concentricity?

[JasonBModerator @jasonb]

Hold one end in your 4-jaw and make a simple plug to go in the other bore with a ctr drilled hole so you can support with the tailstock

The bit with teh blue ink on is the plug

Or if you want access all round open the chuck up into the bore and plug the other end, I did not bother with round but just turned a bit of flat ali.

Edited By JasonB on 01/12/2018 12:36:30

[HOWARDTParticipant @howardt]

I have machined cylinders for my 3 1/2' Evening Star from cast iron bar. With the shape required marked out on the end faces I removed the bulk of material by merely holding it in the vice and stepping the cutter up and over, then angling it to join the steps. Final finish was with a file and Dremel sanding discs.

[duncan webster 1Participant @duncanwebster1]

If you do you want to do it on a mandrel, I've had success by machining a close fitting mandrel, but not interference then having an o ring squeezed axially to grip. With my machining skills getting it to grip but not get stuck by traditional means is a non starter. If you adopt this approach, make it fit the larger bore first, unless you are confident of getting both bores exactly the same

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