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Myford super 7

When to use clutch

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Steviegtr17/01/2020 13:55:47
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481 forum posts
126 photos

Many thanks for the support & advice given above. Picking out from some of your comments. I should have put a centre in the tailstock, My tool height was a tad low, Possibly wrong tool for the job, Not sure on metal & yes it was some scrap from autojumble.Some form of mild steel but no idea what grade. I think I was running at around 600rpm. Too slow with cross feed which i could have set the QC gearbox for a slowish speed but did not. Turning wheel by hand erraticaly. RED L plate stuck on forehead. My wedge type toolpost should be here in a few days so I can then use the 1/2" HSS tools i have, which will not fit mine at moment. Again thanks for the input. Going to fit the replacement speed pot which has just turned up. Trashed the 1st one with too much heat from soldering iron trying to tin the tags. One last question before i ask a load more. When cutting along at say 004" from right to left. Do I draw the tool away to return or just cut back from left to right . Backwards & forwards or cut one way only. ???

Steviegtr17/01/2020 23:31:31
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481 forum posts
126 photos

Getting betterHad another go this afternoon, a bit better. The centre made all the difference too. Thanks for the advice. Still not sure what the steel is but it has a black stripe down it. The tool was home made. I have a good 6" double end grinder but need a good wheel for sharpening drills & cutters . Any idea which wheel I need. Guess fine but what sort.

HSS tool.

Edited By Steviegtr on 17/01/2020 23:32:27

Paul Kemp18/01/2020 00:45:50
383 forum posts
18 photos

0.004" is in finishing cut territory, it's a mere kiss. In fact a cut that small is not great generally with anything carbide unless using one of the polished aluminium style tips. If you have taken a cut of that size and the tool is sharp it shouldn't cut anything bar maybe rubbing moving back. With everything set right you should be able to take a 0.050" cut without too much stress for roughing if you have a bit of free cutting stuff. When roughing out I generally take as big a cut as the job / machine will stand and approaching size decrease the size of cut to end up with a finishing pass between say 5 and 10 thou dependant on tool and material. On the myford the lead screw is generally left set up at 0.004" per rev (because I don't have a quick change box on it and I am lazy swapping change wheels!). Depends on the material and tool but usually roughing I just wind the saddle back to the start and put on the next cut, final pass I note the reading and back it off before winding the saddle back. Hope that helps. You will develop a feel for what's right and what works in time.

Too fine a wheel will load easilly and require regular dressing, I have a "medium"' standard wheel one end of my grinder and a green grit the other which covers all my off hand grinding needs for HSS lathe tools and drills and brazed carbide lathe tools.

Paul.

Hopper18/01/2020 01:12:16
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3989 forum posts
85 photos
Posted by Steviegtr on 17/01/2020 23:31:31:

Had another go this afternoon, a bit better....

HSS tool.

Edited By Steviegtr on 17/01/2020 23:32:27

Hard to tell from the glary pic but that does not look like a suitable tool for turning steel. It looks more like a form tool for brass. It appears to be dead flat on top. Tool for steel needs at least 10 degrees side rake on the top surface. And the tool shape with large flat on the nose is what you don' t need.

You don't need special wheels on your grinder to grind HSS bits. The wheels that come standard on common hardware store grinders are suitable. Usually one wheel is coarse for roughing and the other is more fine for finishing.

You need to look up "knife tool" to get an idea of the shape of tool required. I'll see if I can dig something out and post it for you, but Sparey's book "The Amateurs Lathe" is invaluable for this stuff.

Agree with you that the red painted brazed tip carbide tool is not the best for your little lathe. You might try it again with tailstock centre and see. But usually the flat top surface and reduced clearance angles on them require a more rigid lathe than a Myford.

And I wouldn't be too quick to convert to 1/2" HSS tooling. It takes a lot more grinding to make a toolbit. I go the other way and use 5/16" HSS set on a piece of packing strip in my Myford. Much quicker to grind up.

Hopper18/01/2020 01:25:07
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3989 forum posts
85 photos

OK. Here's a pic of a basic, common "knife tool" used for plain turning of steel as you are doing.

knife tool picture.jpg

The angle on the top surface is about 10 to 20 degrees.

The clearance angle on the leading edge (the side of the HSS toolbit) is about the same, as is the angle on the front surface.

There is more detail and how-to here **LINK**

Disregard what they say on the link about "back rake" on the top surface. You don't need it on small lathes like your Myford. I never use it on my HSS toolbits, and they will take .100" deep cut and give good finish on finer cuts. So you angle the top surface sideways as in the pic above, but not backwards as in the drawings on the link.

And to start with, you don't need the large radius on the cutting point of the tool as shown in the link. Just grind it straight like in the picture. You can later add a small radius to that corner by rubbing the toolbit on a bench oil stone, the type used for sharpening knives and chisels etc.

Clear as mud? Good. You'll get there. Keep experimenting.

Edited By Hopper on 18/01/2020 01:32:49

Steviegtr18/01/2020 02:03:26
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481 forum posts
126 photos

Thanks for that. I have a few new blanks that I can experiment with. I will try your cut on Sat & see how I get on. Many thanks again to all. Do I use cutting fluid or leave it dry. What spindle speed would you recommend for mild steel. Alloy & stainless. 

Edited By Steviegtr on 18/01/2020 02:04:30

Hopper18/01/2020 02:42:12
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3989 forum posts
85 photos

400rpm for mild steel 1" diameter. Halve the diameter and double the speed. Double the diameter and halve the speed. etc etc.

Aluminium and brass, about double the rpm for steel.

Stainless, slow down a bit and see. Maybe a 25 per cent reduction in rpm. I would not mess with stainless at this stage. It can be a PITA. Work-hardens as you machine it.

No cutting fluid needed for general work on Myford scale. It's nice to extend tool life but not necessary.

For screwcutting, use ordinary lubricating oil, engine oil, hydraulic oil etc.

WD40 for cutting aluminium.

Oh, the other thing with toolbits is to minmize the distance it sticks out from the toolpost. Less leverage = less deflection = less chatter.

Steviegtr18/01/2020 23:39:32
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481 forum posts
126 photos

Thanks for the input. I have had some great tips from forum members.

Steve.

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