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Pressure Turning

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Ron Laden24/03/2021 18:35:21
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2297 forum posts
452 photos

Pressure Turning..? something new to me but I watched a Joe Pieczynski video where he covers the method to produce thin discs to a given size.

I have some 150mm x 3mm alu discs to make and it looks ideal but it does raise some issues re safety, he states on more than one occasion that it can be dangerous.

He emphasises the need for a rigid machine so I wouldnt want to attempt it on a small mini lathe but I think my Warco 918 has reasonable rigidity and wonder if its worth a try. He used a sizeable lump which he called a back plate in the 3 jaw and a slightly smaller one in the tool post on a live centre with the thinner disc sandwhiched between the two, relying on the pressure applied from the tailstock for grip and drive.

Just wondered if anyone uses this method and their thoughts good or bad.

.

bernard towers24/03/2021 18:45:02
578 forum posts
109 photos

Yes I have done this in the past but your blanks need to be close to size as depth of cut has to be quite small but yes it does work

paul rushmer24/03/2021 19:15:53
90 forum posts
11 photos

Hi Ron I occasionally use this techneique the trick for me is to use a largish face plate/stub of material in the chuck with a thin rubber sheet 3mm glued on then the work then the pressure plate with a large centre in it of simmilar diameter with a 6 to 9mm thick rubber sheet glued on then the rolving centre. using this set up you can watch the thick rubber swell under load and keep an eye on it while working.

Hope this reassures you Paul

Neil Wyatt24/03/2021 19:39:28
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18994 forum posts
734 photos
80 articles

Is this any different from spinning?

You can spin onto a template.

It puts very heavy demands on the lathe.

Covered in detail by many older textbooks, rarely in the magazines. Regular annealing and smooth tools seems to be the secret, can't say I have tried the technique.

Neil

Rod Renshaw24/03/2021 20:10:44
376 forum posts
2 photos

Hmm... The OP seems to be asking about making flat discs by trimming the edges of a rough blank with ordinary turning tools, something that can be done with the methods listed above.

"Spinning", as I understand it, is forming a bowl like shape ( or a loco chimney top) from a flat disc by pressing the rotating disc against a former using a smooth ended tool to force the disc into a 3 dimensional shape. This requires a lot of pressure and a substantial lathe.

Rod

Jeff Dayman24/03/2021 20:54:23
2223 forum posts
47 photos

Beware of yout ubers showing exotic processes that are hard on equipment. Chances are you can do any job several other ways that are simpler and easier on your machines.

Same goes for the yout ubers chasing millionths of an inch measurement or grinding oilstones and surface plates for sub-tenths of a thou accuracy - sure it's a neat mental exercise and skill test but you can have just as much or more fun building steam and other engines and many other things with nothing needing anywhere near sub-thou accuracy.

Life is short, have fun with semi worn out junk! (as much of my equipment is)

Roger Best24/03/2021 20:59:33
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369 forum posts
56 photos

Just don't stand in the way! smiley

A common technique I will undoubtedly try someday. I am pretty sure the trick is to minimise cutting forces, that means tiny feeds, sharp tools, cutting off a ring, etc, etc.

3mm sounds a bit chunky, but I don't see why not, just work across the face maybe having cut off the excess with a jigsaw.

As it is saving a huge amount of filing time I am sure its worth being careful.

Martin Kyte24/03/2021 21:04:51
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2728 forum posts
48 photos

Depends on how deep you want to go. I have done lenticular pendulum bobs on a Myfordwithout too much effort but they are very shallow.

regards Martin

Bizibilder24/03/2021 21:08:51
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120 forum posts
7 photos

Maybe worth trying the "superglue chuck" method - make a flat plate and superglue your workpiece to it (it helps if you turn a few grooves in the flat plate first to help the glue "set". Then use a tailstock mounted revolving centre with a pressure plate to make sure that your workpiece cannot possibly move. After turning you can break the superglue bond with heat - if necessary use the kitchen cooker - you only need to get to about 150 degrees C or so to break the bond.

Edited By Bizibilder on 24/03/2021 21:09:12

Andy_G25/03/2021 00:07:01
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167 forum posts

100mm diameter x 2mm thick aluminium x 2 pieces on a Chinese 7 x 14 lathe the other week:

The disks were cut roughly to shape with a jigsaw first, and the protective film was still on the sheet which I think helped with drive. No problems encountered, I would use a bigger backplate next time (this was just a scrap of 40mm bar that I had to hand, I think. )

They came out very well IMHO:

Good enough for my welding, anyway!

Edited By Andy_G on 25/03/2021 00:17:33

Mike Hurley25/03/2021 09:06:27
305 forum posts
87 photos

Nice welding job with Aluminium Andy!

Andy_G25/03/2021 11:00:36
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167 forum posts
Posted by Mike Hurley on 25/03/2021 09:06:27:

Nice welding job with Aluminium Andy!

Thank you!

I was pleased with it - TIG is very satisfying when it goes well (and equally frustrating when it doesn’t!).

Circlip25/03/2021 11:44:22
1502 forum posts

Have a disk of chipboard fastened to the faceplate on my Maximat. "Disks" to be cut are glued to this with double sided tape and a "pressure" pad with a centre drilled in it pushed onto it with a revolting centre in the tailstock. Basically "Trepanning" but keeping the centre disk. Make sure the cut diameter is fully supported on backing plate, ie. to cut disk 100mm dia. backing disk should be at least 120mm dia.

As an apprentice, it used to get exciting trepanning ring guages from 3/8" gauge plate.

 Weapon of choice for turning is a parting tool fed from cross slide.

 

Regards Ian.

Edited By Circlip on 25/03/2021 11:46:35

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