ME 4552 page 149

I quote from the beginning of this text about making The Middleton V-4 Oscillating Cylinder Engine:

Machine the crank discs from a piece of 2 inch or 50mm diameter steel. Place the metal in a four-jaw chuck, but in one jaw, place a 15 mm thick packing piece (for the throw) (photo 15).
Clock the bar to make sure it is running true, turn to 45mm diameter ...

The picture (No 15) shows the bar concentric with the tailstock centre, and in line with the lathe bed.

Running true to what? And how can the bar be in line and offset 15mm while lining up with the tailstock?

Sorry, I just don't get it

Cheers, Tim

Tim, have a look at this post about the middleton from yesterday.

If you read on he then says undo 3 jaws leaving the one that had the 15mm packer untouched, remove the packer and then retighten the other 3 jaws. This will have the effect of offsetting the bar by 15mm so the pin hole can be drilled and reamed

Edited By JasonB on 17/01/2017 18:54:59

What a strange way to set something in a 4 jaw. Unless the jaws shown top and bottom are tightened equally the offset won't be 15mm anyway (it won't be far off admittedly). If I didn't mind a small error I'd use a bar square to find the centre, centre punch off centre and set up to the punch mark. If I wanted it more accurate I'd do as above then fine tune using a DTI

Mount DTI on cross slde touching work

establish max as in picture above, rock spindle to and fro to get exact max

set DTI to zero

move the cross slide back by 15m and check min position.

If DTI not zero adjust and repeat

I use Tubal Cain's method where you calculate teh size of a spacer from a slice of a suitable bar

Neil

It is a pity that nowhere does it say anything that hints at this odd (to me) way of determining where a hole should go. The words 'Take the ... packing out, tighten the three jaws up, drill and ream' might have continued 'to make the hole for the crank pin.

Is it not possible (or even easier) to part off the three discs and Then drill a centre hole in each, fit a tight pin, and drill the offset holes together? The idea of offsetting a chuck jaw and relying on that to position the offset hole, is what seems odd. It would even have made more sense (to me) if the jaws had all been in contact with the bar for the hard work of turning and parting off, and the required offset had been achieved by using the 15mm piece to create the offset as the next operation.

Looking at the whole article, the major confusion (for me) arises because of the extreme brevity of the instruction. The three words 'for the throw' carry the whole burden of explaining the sequence. 'Drill and ream' adds nothing as we are not told what the hole is for. But the actual effect was to sow the seeds in my mind of turning the crank from solid.

I am obliged to Duncan for agreeing that the method was strange, but I make no sense of the comment by Neil that he uses 'Tubal Cain's method' without any clue as to where one might learn more about what this method was (or which Tubal Cain he meant).

Cheers, Tim

There was only one:- Tom Walshaw. Any later incarnation is an imitation.

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... What of the original incarnation ?

MichaelG.

https://en.m.wikipedia.org/wiki/Tubal-cain

Edited By Michael Gilligan on 18/01/2017 00:16:59

Tim do you only read the text and not look at the photos and drawings? From these it is obviuosly a built up crankshaft.

If we were to need word for word descriptions of every single step of machining a part the articles would run for months, authors have to assume that people making these engines have some ability to think for themselves and relate what is said in the text to the drawings.

As I said in the other thread I could follow what was being described but not how I would persomally have done it. Probably face the end of the bar and then set height gauge on cross slide, mark ctr height then rotate chuck 90deg and put a second line 15mm above ctr. Punch with optical punch and then set punch mark to run true.

The text as sent in for this article was very hard to follow as were the sketches, Diane (and helpers) have had to re-write a lot of it and alter drawings, think she has done well as a non engineer.

J

The only time I would use packing like that is if I was going to off set a piece in a THREE jaw chuck, part of the idea of a four jaw chuck is that you can off set an item with out packing.

Ian S C

I agree, this makes much more sense to me. Definitely the direct route.

Michael W

There are also a number of errors that could lead to the beginner to have to remake some parts. Not having got the last part of the article yet, I have made up the crank and some other parts using what material/sizes I had.

As the instructions for crank assembly were not available yet (to me!) I made the discs from 13/4 bar, turned to diameter and centre hole drilled and reamed, then transfered to the mill/drill to drill the offset holes( I have cheap dro's on the mill)

A pet hate of mine is when the auther says he used various bits of scrap lying about in the workshop rather than having to go out and purchase same. I nearly died of heart failure when I priced up 6mm brass sheet!!!

I did not particularly like the method of cylinder construction so made mine out of 25mm hex bar, only parts left to make now are the end caps for the cylinders, otherwise the engine has been run in as is by driving the main shaft.

Next step is strip down, clean, reassemble and try putting some air through and see what happens. Interesting but enjoyable build at my level of competence(quite low I must admit), and managed to spot the mistakes before parts were ruined. I did manage to get hold of the original ( middleton v4) construction notes which helped fill in some of the gaps while waiting for the magazine to catch up.

Ouch..Yeah that isn't good. I found it bad enough just buying 1/8th brass sheet.

This could be "scrap" from material used on a paying job rather than completely out of their pocket.

When I think of scrap, it's more like the hundreds of little pieces of BMS round bar I have lying around rather than "prized-almost-off-the-shelf" material!

If you want to really end up in A+E then have a look at copper 1/4 sheet.

Edited By Michael-w on 18/01/2017 09:22:02

You have both obviously got very long cross slides to be able to move them 15m

Also should you not be seeing 30mm of total movement which would equate to 15mm on the dial if the cross slide were moved back 15mm.

If you are going to do it with a dti on the OD then a 0-50mm plunger type would be best and adjust the work until you see 30mm of movement, eliminates any errors in moving the cross slide and save having to wind it in and out a number of times. Both methods would only work with the dti spot on ctr height or maybe use an elephants foot end

J

Edited By JasonB on 18/01/2017 11:51:12

Page 13.12 in 'The Model Engineer's Handbook' by 'our' Tubal Cain.

I doubt the USA version was deliberately ripping off the pen-name, it's a fairly obvious one.

Neil

you're absolutley right, it should be 30mm, I forgot to double it. If you have a DTI with 30mm stroke by all means, none of mine do.

PS Mark Rand is wrong about Tubal Cain. He wasn't the only one or even the first. I suggest that a glance at Genesis may be fruitful. Of Wiki if you are without.

Cheers, Tim

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... or even a glimpse back at my post of 00:16:28 this morning

MichaelG.

I'm sure the USA fellow was totally oblivious of the UK Tubal Cain when he chose the moniker for himself. Not much news from the outside world penetrates the borders over there, but the Bible is widely read so he would have come across the original original in Genesis more likely.

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Paragraph headed: 'Eccentric Turning in the 3-Jaw Chuck'

MichaelG.

Slight amendment to my last post, sometimes if the item to be off set in the 4 jaw is under a certain size, a bit of packing is needed on the jaw that is closed nearest , or across center, so that it doesn't foul on the jaws either side of it. Another way around the problem, and also to solve the problem of material too small for the 4 jaw to close on is to make a collet, just a bit of bar with a hole through it, and a hacksaw slot cut through one side(and if it's too stiff, half way through the other side).

Ian S C