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Surface finish

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Adrian Harrison02/01/2019 21:07:26
38 forum posts
11 photos

I bought an older Drummond m type lathe a few months back and i am having problems with getting a good surface finish..
at the moment I am turning down some bolts to make a wheel adaptor for my rc truck and the surface look like its ripping out, would this just be the cheap bolt material doing this?

Martin Connelly02/01/2019 21:15:55
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847 forum posts
99 photos

Bolts are not often machined from solid. The bar stock is cut off and one end heated then swaged out to form the head. This requires material suitable for this process and it also sets up a variable grain structure in the bolt. As a result bolts do not make good raw material as you are finding out.

Martin C

SillyOldDuffer02/01/2019 21:24:09
4521 forum posts
971 photos

Yes, it could be the bolt. Not necessarily because the bolt is cheap, just that the alloy used to make it may not be easy to machine. (Bolt designers are unlikely to allow for amateur turners in their calculations and might well use metal unsuitable for your needs I've had bolts that machined well, and others that were vile.)

There are other possibilities if you're a beginner: wrong depth of cut, feed-rate, rpm, tool height, &/or tool profile. Have you tested the lathe by turning a known metal rod yet? It may be the lathe is faulty (shot bearings or badly worn) or needs adjustment (tighten the gibs), set the tool height, support the job etc.

If you can provide more detail forum members are good at working out what's going wrong.

Dave

Adrian Harrison02/01/2019 21:50:01
38 forum posts
11 photos

I will try a bar stock that i have tomorrow on the lathe and see if thats better.
i am thinking that its basically the bolts that are the problem after what martin has said and maybe i need t think of a better plan..
i changed my feed rate from the lowest to highest and it did get better but I'm thinking my lathe being an older 3 speed pulley just is not fast enough

Adrian Harrison02/01/2019 22:05:53
38 forum posts
11 photos

what is the best tool profile for what i am trying to do?

not done it yet02/01/2019 22:24:00
3145 forum posts
11 photos

The one thing that SOD omitted was: what cutters are you using? Some bolts may also have been heat treated.

More info required, yet!

Ady102/01/2019 23:55:11
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3463 forum posts
513 photos

Learn how to check and adjust your headstock bearings

Use your tailstock, a live centre most of the time and a dead centre for critical stuff

Learn how to check your slide and saddle and adjust them

Every tiny error is your enemy, took me a couple of years to master my machine

Then there's the tooling.... and the material

bolts can be a bit weird for the reasons mentioned above, carbide tools tend to work best

Stiffness is often more important than speed

Edited By Ady1 on 03/01/2019 00:02:05

Hopper03/01/2019 00:01:48
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3651 forum posts
72 photos

A common cause of finish problems on the M type is too much slack in the headstock bearings. They are a tapered bronze bushing with slotted ring nut. One at each end of the headstock. Trick to adjusting them is you have to first slacken off the two oiler bolts that stick up from the headstock. Then tighten the ring nuts with a C spanner until the spindle can be felt to drag quite a bit. Then when you nip up the two oiler bolts they expand the bronze bushings out into the tapered housing and the spindle frees up just that little bit. Sometimes takes a few goes to get the setting just right.

Also, setting the gib strips correctly on the carriage, cross slide and top slide helps with better finish too.

For any steel half inch diameter or smaller, usually use the fastest speed pulley. If the chips are coming off blue and smoking, slow it down one pulley.

But do your tests with a known piece of plain mild steel bar before getting too involved.

Edit: Ady1 beat me to it while I was typing. But you can see the headstock bearings adjustment is a common cause of poor finish on these lathes.

Edited By Hopper on 03/01/2019 00:04:48

duncan webster03/01/2019 00:37:29
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2161 forum posts
27 photos
Posted by Martin Connelly on 02/01/2019 21:15:55:

Bolts are not often machined from solid. The bar stock is cut off and one end heated then swaged out to form the head. This requires material suitable for this process and it also sets up a variable grain structure in the bolt. As a result bolts do not make good raw material as you are finding out.

Martin C

When I worked for Greenwood and Batley they made machines for cold forming the heads on bolts, wire in threadless bolts out. Cold was relative, as a new starter I was invited to pick one out of the skip, bl**dy hot let me assure you

Adrian Harrison03/01/2019 02:42:38
38 forum posts
11 photos

Thanks for all the replys much appreciated, I will start tomorrow buy adjusting the head stock bearings..

I will also buy a live center as I only have a dead center at the moment..

The k you Hopper for explaining how to adjust the head stock bearings

Hopper03/01/2019 03:46:25
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3651 forum posts
72 photos

You're welcome. There is a wealth of info, including a cross-section of the headstock bearings that makes things clearer here https://groups.yahoo.com/neo/groups/myfordlathes/info

It's the Yahoo Groups group for Drummondlathe. In the FILE section there (you have to join to access it, free) are copies of the original manuals etc and lots of other good info.

A good book for getting started on these vintage lathes is the vintage book "The Amateur's Lathe" by LH Sparey. Still in print and widely available from booksellers and model suppliers. His instructions for grinding a "knife tool" that works particularly well on these old machines are the clearest and easiest to follow that I have seen.

Live centre is a good idea as these lathes do benefit from its use. The headstock spindle diameter is a bit smallish so heavy cuts - say .100" deep on 1" bar etc - will cause it to flex a bit without a centre. You can use the dead centre ok, just keep it well lubricated with moly grease etc.

Edited By Hopper on 03/01/2019 03:50:20

Adrian Harrison03/01/2019 04:44:31
38 forum posts
11 photos

I will order that book tonight and I'm sure I should have a knife tool in all the hss tooling that came with the lathe

Ady103/01/2019 09:09:29
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3463 forum posts
513 photos

I made my own live centres, one of my first projects

Bought a pack of cheap bearings from ebay for the job, they aint brilliant but I still use them 10 years later

Buy a DTI with a magnetic stand for 20 quid, you'll definitely need it before long

Enjoy and GL

Edit: I did a headstock stripdown here. Take your time and enjoy the learning of new skills

Edited By Ady1 on 03/01/2019 09:13:52

Mick B103/01/2019 09:37:36
1124 forum posts
62 photos
Posted by Adrian Harrison on 02/01/2019 21:50:01:

...

...but I'm thinking my lathe being an older 3 speed pulley just is not fast enough

With a decent HSS tool, there's practically no such thing as not being fast enough. Sometimes finishing and screwcutting is done at speeds of 10 M per minute or less, or even by hand-rotating the spindle or chuck for some tasks.

Adrian Harrison03/01/2019 16:33:44
38 forum posts
11 photos
Posted by Ady1 on 03/01/2019 09:09:29:

I made my own live centres, one of my first projects

Bought a pack of cheap bearings from ebay for the job, they aint brilliant but I still use them 10 years later

Buy a DTI with a magnetic stand for 20 quid, you'll definitely need it before long

Enjoy and GL

Edit: I did a headstock stripdown here. Take your time and enjoy the learning of new skills

Edited By Ady1 on 03/01/2019 09:13:52

thanks for the link Ady1, just about to sit down with a morning coffee and read the whole thing..
and making my own centres is something that i have thought about doing, as you say it would make a good first project and i have my eye on a DTI and magnetic stand at my local tool shop

Adrian Harrison03/01/2019 16:37:23
38 forum posts
11 photos
Posted by Mick B1 on 03/01/2019 09:37:36:
Posted by Adrian Harrison on 02/01/2019 21:50:01:

...

...but I'm thinking my lathe being an older 3 speed pulley just is not fast enough

With a decent HSS tool, there's practically no such thing as not being fast enough. Sometimes finishing and screwcutting is done at speeds of 10 M per minute or less, or even by hand-rotating the spindle or chuck for some tasks.

Screw cutting, now there is a discussion! I was just thinking if i had a bit more speed then i may get a better finish but from all the points people have made here I'm thinking not...
I have a full set of gears with my M type so screw cutting is something I will try

larry phelan 103/01/2019 17:25:14
458 forum posts
11 photos

Not sure that you need much more speed for screw cutting ??indecision

Adrian Harrison03/01/2019 18:20:50
38 forum posts
11 photos
Posted by larry phelan 1 on 03/01/2019 17:25:14:

Not sure that you need much more speed for screw cutting ??indecision

not for screw cutting no but for turning

Howard Lewis03/01/2019 20:44:44
2142 forum posts
2 photos

A lot of hardware these days is not screwcut, but the threads are rolled. And if the bolt is high tensile, it will be hard, and dislike being cut.

How hard/tough? 1/2 UNF bolts in W Range put into yield at a tensile load of 9 tons!

I have changed a few of those from bolts into setscrews, with a die. Good cardiovascular exercise, and definitely wet shirt territory.

If there is any manganese in the spec, it is likely to work harden, as you cut. The first cut may be O K but the following ones won't be! If you can get the speed high enough, carbide may do the job. But you need to have everything spot on to succeed.

Howard

Ady104/01/2019 00:10:11
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3463 forum posts
513 photos

I've uploaded my entire drummond headstock stripdown here

Some photos are rubbish but a lot are useful

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