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Myford M - a few random questions

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Nicholas Wheeler 103/07/2022 11:19:33
959 forum posts
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I'm about to make 2 left and one right of these from 10x20 steel and 1/8" bits:

tangential tool holder v1.jpg

SillyOldDuffer03/07/2022 13:34:26
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Posted by Alec Gunner on 26/06/2022 15:38:51:

...

The information about carbide inserts is particularly interesting - I am not very good at grinding up HSS and whilst I am sure I will improve, I will waste a lot of time and material (or do a lot of filing to restore surfaces) in the meantime, so inserts would make life considerably easier.

Based on the suggested information it appears to be possible to take much heavier cuts than I was expecting which would be good news if true, although 0.1mm per pass is what I am used to so can live with it.

Alec

I prefer inserts to HSS for exactly the reasons Alec gives: they potentially eliminate the need to buy a grinder and learn how to use it. Not everyone is good at grinding, so beware folk to whom it came naturally: they insist it's easy and just needs a bit of practice. Yeah right, so does learning Integral Calculus...

In practice I use both, 80% inserts, switching mainly to HSS when an unusual tool profile or very fine cuts are needed, or I'm having trouble getting a good finish.

Carbide is fussier than HSS about depth-of-cut, feed-rate and RPM. Works best when pushed hard at high-speed, removing metal 3 to 12 times faster than HSS. Though sharp Carbide inserts work well enough for most purposes, hobby lathes don't have the power, speed or rigidity needed to get industrial performance out of them.  I still prefer inserts!

Assuming the drive-train and cutter are both in good order and the gibs are adjusted, depth of cut depends mostly on the power of the motor and the material. Rule of thumb, 1HP will remove 1 cubic inch of mild-steel per minute.

I suppose maximising depth of cut might be useful when roughing out, but even though my lathe can do it I rarely take cuts more than 2mm deep (4mm off the diameter). Though there are exceptions, I find it more civilised to take cuts between 1 and 0.1mm deep, less for finishing.

Best thing to do is experiment. Get some free-cutting mild-steel bar, at least 25mm diameter. Set RPM to 10000/25 = 400 (this is about right for HSS, triple RPM for carbide if the machine can run that fast), and try taking various depths of cut over a 30mm length with a sharp tool, with minimum overhang in the tool-post.

Listen and observe. The machine should sound as if it's definitely working hard but not in distress. Nothing should be bending, lifting, twisting, or otherwise misbehaving mechanically.  Look for the best compromise between quick metal removal, controlled accuracy and good finish.

Once depth-of-cut is understood, experiment with feed-rate in the same way.

Friendly materials cut well over a wide range and are very forgiving. Difficult materials are much fussier about using the right shaped tool and getting all three parameter spot on. Some are impossible.

If you're a man in a hurry, beware of fitting a giant motor to remove metal extra-fast: the drive train will wear rapidly, and accuracy goes to pot when the frame is twisted by excessive torque. Damage done by a crash is much worse too!

By the way, don't expect to file HSS - it's too hard! Grinding is the answer.

Dave

Edited By SillyOldDuffer on 03/07/2022 13:41:51

Hopper03/07/2022 23:55:28
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Posted by SillyOldDuffer on 03/07/2022 13:34:26:
 

I prefer inserts to HSS for exactly the reasons Alec gives: they potentially eliminate the need to buy a grinder and learn how to use it. Not everyone is good at grinding, so beware folk to whom it came naturally: they insist it's easy and just needs a bit of practice. Yeah right, so does learning Integral Calculus...

When I was in high-school, every 15-year-old boy could grind a lathe tool bit, sharpen a drill bit and a plane blade. Was part of the metalwork/woodwork class that all boys took. I don't remember any boy who could not master all three skills in fairly short time.

It;s not rocket science, or even integral calculus.

 

Edited By Hopper on 04/07/2022 00:06:09

Jon Lawes04/07/2022 07:29:58
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995 forum posts
Posted by Hopper on 03/07/2022 23:55:28:
Posted by SillyOldDuffer on 03/07/2022 13:34:26:

I prefer inserts to HSS for exactly the reasons Alec gives: they potentially eliminate the need to buy a grinder and learn how to use it. Not everyone is good at grinding, so beware folk to whom it came naturally: they insist it's easy and just needs a bit of practice. Yeah right, so does learning Integral Calculus...

When I was in high-school, every 15-year-old boy could grind a lathe tool bit, sharpen a drill bit and a plane blade. Was part of the metalwork/woodwork class that all boys took. I don't remember any boy who could not master all three skills in fairly short time.

It;s not rocket science, or even integral calculus.

Edited By Hopper on 04/07/2022 00:06:09

I can sharpen HSS, but find carbide suits most things I need to do. As mentioned, it's useful for unusual shapes or form tools, but for the most part my pile of HSS cutting tools is gathering dust.

I'm sure most people could operate a treadle lathe rather than an electric motor, but who wants to do that if there is a better option?

Hopper04/07/2022 08:00:29
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Posted by Jon Lawes on 04/07/2022 07:29:58:
Posted by Hopper on 03/07/2022 23:55:28:
Posted by SillyOldDuffer on 03/07/2022 13:34:26:
 

I prefer inserts to HSS for exactly the reasons Alec gives: they potentially eliminate the need to buy a grinder and learn how to use it. Not everyone is good at grinding, so beware folk to whom it came naturally: they insist it's easy and just needs a bit of practice. Yeah right, so does learning Integral Calculus...

When I was in high-school, every 15-year-old boy could grind a lathe tool bit, sharpen a drill bit and a plane blade. Was part of the metalwork/woodwork class that all boys took. I don't remember any boy who could not master all three skills in fairly short time.

It;s not rocket science, or even integral calculus.

 

Edited By Hopper on 04/07/2022 00:06:09

I can sharpen HSS, but find carbide suits most things I need to do. As mentioned, it's useful for unusual shapes or form tools, but for the most part my pile of HSS cutting tools is gathering dust.

I'm sure most people could operate a treadle lathe rather than an electric motor, but who wants to do that if there is a better option?

But that doesn't mean you should throw the baby out with the bathwater and not have a bench grinder at all, throwing away drill bits as soon as they get dull and leaving yourself unable to make up special purpose lathe tools such as form tools or others as needed from time to time. And if you really want to get the best off-tool surface finish and sub-one-thou accuracy on a small lathe, good HSS tooling is superior to even the ground inserts.

(BTW I am with you in that I can grind HSS tools but these days use carbide for 75 per cent of work.)

Edited By Hopper on 04/07/2022 08:02:09

Jon Lawes04/07/2022 08:02:46
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995 forum posts

I agree.

Alec Gunner09/07/2022 11:42:45
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4 photos

Thank you for the further comments on tool design/selection. The thread has wandered (as they do) but for me it's all useful information as I set myself up to use the lathe rather than just fix it.

The C spanner has arrived, the spindle has been removed and the bearing realigned. A bit of head scratching as to how to turn it but a drawing courtesy of David George indicated that the bearings are externally conical so re-fitting the locking ring and tapping the bearing back using a wood block had it loose so I could rotate it. Fortunately the wedge is still present.

I also realised that the wedges have to be inserted from the inside, and that removing the spindle alone does not allow the pulley cone to be removed from the headstock as it won't clear the casting without also removing the back gear. Fortunately everything is clean and smooth, and none of the thrust bearing balls dropped out, so I decided to leave that alone and simply reinsert the spindle.

I have also dressed out the worst of the abuse on the locking ring slots - mostly it was possible to 'forge' it back into place. They are still a bit ugly but much better than they were.

I will make up a temporary oiler bolt today and get it set up and running. Assuming everything goes well I can then look to make some proper drip oiler bolts and the other short-term need to is to machine a register on a faceplate which I have picked up that has the correct thread but no register, and then probably purchase a backplate for a 4-jaw chuck (having now bought a suitable Burnerd chuck) and do the same.

I might eventually manage to use the lathe to make things other than for the lathe itself - otherwise this could become a self-sustaining project in its own right!

Alec

Hopper09/07/2022 11:46:04
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6695 forum posts
347 photos

Ah yes, making tools to make tools to make tools is a well known hobby! Enjoy.

Ady109/07/2022 13:13:58
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738 photos

This is where mobile phones finally come in useful

If you strip down an unfamiliar bit of kit video the process with a phone and reassembly becomes a doddle

Howard Lewis10/07/2022 02:44:46
6314 forum posts
15 photos

As Hopper says, you are on the slippery slope already!

But it all good practice and experience., which will, as we say "Come in handy, one day"

Howard

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