toolpost material

A while ago someone was asking here about the best material to make a lathe toolpost from, but I can't find the thread. Anyone remember what happened,
or have a suggestion for a suitable material?
I am only making one, perhaps two, unlike the OP who iirc was making lots. Got to be quite tough though, it's a bit thinner than normal to fit a large tool, I made one from CI (meehanite) and it broke.
Toolpost is 44 mm x 44 mm x 32 mm, if anyone has something suitable in their scrap box I can swap some beer tokens. Or if anyone has a 4-way toolpost for a C3/Conquest/7x12 type lathe that would probably do.
ta,
--
Peter Fairbrother


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Peter Fairbrother wrote:

What you have to consider is metal in that size is hard to get hold of for nothing. But mild steel in that size is readily available and is tough enough in my opinion for a tool post. I made a couple of tool posts and tool holders out of mild ......they are holding up OK. also it doesn't distort when machining like cold rolled bright does. fabricators have this size in....there will be plenty of off cuts in their scrap bins.
The only thing bad about the stuff is that its quite hard on your endmills and not always consistent in finish or dead on square in it's raw state...........but if you have a surface grinder ....you can make the stuff look real well.
Treat it like a piece of wood ("plained all round") and get it "square all over" before you attempt any machining of it into the tool post. That way you remove all the mill scale and have a nice start.
all the best..mark
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mark wrote:

While I am always pleased by "free" :~) , why do you think I was asking for a freebie? Or do you?
Maybe I wasn't clear - I'm only looking for one piece of metal, unlike the chap who wanted to make lots, so materials cost isn't really an issue - I don't mind if it's a bit expensive, or overspecified. Within reason. I have a chunk of 316L stainless for instance, but it seems overkill to use that.
What would be a suitable material? what is normally used?
And afaics no-one sells 4-way toolposts for a Chinese 7x12 minilathe. Plenty of quick-change ones, but no 4-ways. I wouldn't mind paying shop prices for one, even though it's not really what I want - but afaict they aren't available.

I have a suitably-sized chunk of mild steel- in fact I have suitably sized chunks of both bright and black mild steel - but IMO I don't think either is strong enough, especially in this case. I've already broken a good quality cast iron one, and it seems to me that a mild steel one would do no better.
It gets a lot of hammering - it'a for a large parting tool, used for interrupted parts. I can't make the toolpost oversize, it need to be this size because it's used right at the edge of the envelope - I'm parting 90 mm dia stock on a Chinese C3 7x12 type lathe! (Chester Conquest)

I too have made some tool holders for a quick release toolpost from black mild steel, and they seem okay. But they don't take the force this toolpost will have to.

Afaik there are two types of mild steel - bright and black. Both are rolled. reading between the lines, I guess that the black one is hot-rolled, and the bright one is cold rolled - is that correct?
I've only used the black one - is the bright one stronger?

The bright chunk I have is round bar, and would need squaring probably in a four-jaw chuck, and the black chunk is oversize, so no problem there - but I don't think mild steel will do.
Or are we talking about different things?
Thanks,
--
Peter Fairbrother



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Peter Fairbrother wrote:

316 is very unsuitable. It's a mistake to think it's tough stuff it's isn't.
I'd suggest EN8, there's tougher materials, but it depends on what machinery you have to machine the stuff.
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"I've already broken a good quality cast iron one, and it seems to me that a mild steel one would do no better."
HMMM.............. Cast iron is only good because it's a stable metal.....no heat related contraction expansion issues and is good in compression but most of it is about as strong as Blackpool rock when streced...and mostly used because of its cheepness....even the best cast irons only yield 10% before snapping take my word ,on your 7x12 lathe, as long as you have ledges above and below to tool of at least 7mm your not going to bust distort or bugger mild steel up. the tool posts and tool holders I've made are being used on a 2.5 hp smart and brown 1024 lathe............. absolutely no trouble from them at all. I've made a parting off tool holder with the stuff.........and this has to be ridged with no give .........or I would be wrecking my mildly expensive hertel blade and tips plus my work. I was just trying to show you the cheapest most logical route to go down........as I'm not rich..........So I work cheep. of course I would say ,if the tool post ledges happen to be less than 7mm .you do need some special metal. but mild is far Superior to cast iron, as a tool post.
BTW .how is it that you are putting so much force on your post with your parting off tool .....should cut like butter with very little force.............buy a Hertel blade and tips ..you will never look back..honest.
'nother thing I've heard that the top slide needs modifying on them small lathes. some mods here.
http://www.mini-lathe.com/Mini_lathe/Modifications/modifications.htm
all the best...mark
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Parting off blade holder with hertel tool, plus steady rest adaptor ..both made of mild steel. made them last year.
http://img.photobucket.com/albums/v190/aboard_epsilon/smart%20and%20brown/fixedsteady.jpg
all the best.mark
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On Sun, 02 Apr 2006 00:13:23 +0100, Peter Fairbrother

Make it out of mild steel and have either 5 thou of case applied or Tuftrided at your local heat treat place. Tuftriding has the added advantage of being nice looking and rust resistant. I can assure you after making 4 holders and over 60 posts for various lathes this is more than suitable.
As regards not being up to the job a decent designed post will stand far more than a C3 lathe can throw at it.
I have stalled a big TOS lathe 11" centre height with 10 HP motor, wrecked the job, wrecked the tool but the post survived with no problem. I hardly think a 600W C3 is in the same league.
Good god man it's a tool post not rocket science.
When milling the slots use an end mil or slot drill with a slight radius on the corners. It was probably the use of a sharp cornered cutter on cast iron that caused your first post to break by inducing a stress point -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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O

Chronos have this one, don't know if it's any good for your application.
Four Way Toolpost(Reference #FWP1) 2" Square with 3/8 Bore centre hole accepts tools up to 1/2 square
Price inc UK mainland carriage: 13.62 16.00 Including VAT(appl European union only) at 17.5%
I'm sure most of the people who supply far eastern machines will supply spares for them, so you should be able to find something.
I've think I've got an old one off a myford in the corner of the workshop -let me know if it would be any good & I'll look it out for you.
Regards Kevin

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Peter Fairbrother wrote:

Peter, I agree totally with what Mark and John have said, mild steel (either type) is more than adequate for your toolpost. You need to look at the differences between cast iron and mild steel as they are in fact like "chalk and cheese". Cast iron is a brittle material and will fail quickly when subjected to alternating stresses (interupted cuts) particularly if there are sharp corners or rapid cross-sectional area changes in the load path. Mild steel is much more resilient and will, if correctly designed to operate within its' elastic limit, remain unaffected by thousands and thousands of hours of alternating stresses.

This concerns me a little, a correctly designed toolpost will have adequate lands particularly at the top of the tool slot, are you trying to put too big a tool depth within the restricted toolpost height you have available? Parting off 90 mm stock should exert no more force on the toolpost than 25 mm stock if you are setting the surface speed/depth/feed of cut correctly. Can you get a suitably slow rpm to ensure a correct surface speed and sufficient torque with your C3? If you are using tipped tooling and a high speed to part off I would expect a cast iron toolpost of normal proportions to fail quickly. As John says some case hardening would be "nice" but not at all necessary to provide the necessary strength. I would be much more worried about the affects on your toolslides of an operation that is breaking your toolpost.

Peter, this is just not correct, the force exerted on the toolpost is a result of the surface speed/depth of cut/feed rate. If you have set the machine up correctly it will not matter if it is 25 mm or 900 mm stock.

Thats my understanding as well. The cold rolled version has greater internal stresses particularly near the surface that will sometimes cause the material to distort when machined. The rolling process has an affect on the surface structure which is of course slightly different in the two materials and hot rolled is usually more malleable. For your purpose either will do fine.

Like the other replies I have made and used many toolposts for a variety of lathes, I have always used mild steel (cold rolled as that was what I had available) with total success. In fact several are still in use after 15 years or so, battered and bruised but certainly not broken.
Best regards
Keith
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jontom snipped-for-privacy@hotmail.com wrote:

Hello Peter, I noted that you are parting off on an interrupted cut, why not try this idea that worked for me. Install a small high speed Router motor or something similar, fitted with a diamond coated cutting blade and employ it as you would with a parting tool, it gave an excellent finish, if taken through at not too fast a speed. A little ''SCARY'' at first. All the best for now, John.
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On 2 Apr 2006 03:11:27 -0700, jontom snipped-for-privacy@hotmail.com wrote:

<snippage>
<more snippage>
If Peter were referring to a turning or facing operation, you would be right. Remember, however, that in order to part off 90mm dia stock, the parting tool will have to hang out of the tool holder by at least 45mm. This is a lot of stickout and leverage on the toolholder for a small lathe.
Mark Rand RTFM
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Mark Rand wrote:

Yes - as you have to approach the work from the side in order to part off, and the workpiece is so big it fouls the standard toolpost even when the crossslide is as far out as it will go, so you need to use a smaller and shorter toolholder, stressing it even more. And you need to reset the parting-off blade's position in it's holder after every few mm of cut.
- and when you are getting towards the centre and are now going a bit faster, and all 14 pounds of rapidly-rotating chuck and workpiece decides to snatch and jam, then the force and leverage is ... considerable.
Ripped the previous toolpost apart. Stripped teeth from both drive gears. Anyone know a UK supplier of spare C3/ 7x12/ minilathe parts? littlemachineshop.com do the double gears for $6.99 each, but they are in the US.
AS I am now rebuilding the head, is there anything else to do at the same time? Replace bearings perhaps, though the ones I have seem okay?
One piece of general advice to people considering buying their first lathe, from my experience so far - buy a bigger lathe, the one you have in mind is too small. The bigger and heavier the better.
--
Peter Fairbrother


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Peter Fairbrother wrote:

Peter/Mark
Point taken, sorry I'm guilty of assuming that everyone works the same way as I do and I have learnt that is not the case many times, getting old I suppose. When I used my old 918 on a similarly oversized job I removed the topslide and mounted a toolpost directly on the cross slide. It meant that I had to replicate the topslide mounting on the bottom of a large chunk of steel but it worked well although was a bit of a pain to change every time as the cross slide needs removing to fit. Could you not do the same?

When doing my job on the 918, I found it impossible to part off large diameter aluminium without grabbing if I tried to do it with a single tool width cut. I ended up wasting a bit of the scrap material by cutting double width to provide adequate tool clearance. I also used one of the few advantages of a belt drive machine by running the belt fairly loose so that a grab slipped the belt rather than smashed the machine. I also mounted the blade type parting tool directly in my home made toolpost but like you did need to reset at the halfway stage.
I also found that a parting tool stuck out that far bends and does not part straight so had to accept that the part would need facing after anyway. This is the main reason it grabs when parting off. Cutting the double width slot showed just how much it would bend and although I initially thought the single slot would provide support and stop this bending if lubricated well it didn't and I could not stop the grabbing just with lubrication. While this can be minimised by using a tool with a perfectly square end parallel to the spindle this then leaves a "pip" anyway. As soon as you angle the tool to try and part off without a pip or the tool is not set exactly square the tool will always bend when set out this far. I used one of the insert parting tools with the slightly thinner blade holders thinking that it would cure the problem, it did not. I could however get away with a slightly narrower slot but the insert moved sideways in the blade as it is not restrained and jammed or scored the workpiece badly anyway.

I think that this is one of the most important pieces of advice to give to anybody starting out. It is also the advice that is most ignored - I know because I learnt it the same way by buying too small (financial reasons) and having to buy again later.
Best regards
Keith
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jontom snipped-for-privacy@hotmail.com writes

Some machines (I am thinking of the Boxford that I once had) have a rear mounted parting tool post that attaches directly to the cross slide. I can't remember the theory as to why an inverted tool may work better in that position - but I do remember that it did.
--
Mike Hopkins
CSME <http://goto/cheltsme>
  Click to see the full signature.
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Mike H wrote:

Mike
Two reasons really. Firstly as crosslides are virtually always dovetailed, the cutting forces will pull the topslide upwards tightening the fit of the dovetails.
the 2nd reason is the chips tend to fall away instead of jamming up in the groove. Jamming of chips is usually the main reason for parting off to fail. Also one of the reasons for a poor finish on parted face.
On my capstan I always part off from the rear toolpost. Most jobs I part to finished length.
Parting isn't the devil a lot seem to think it is ;-)
My tips are make sure jibs and headstock bearings are tight enough. Those without angular contact bearings in the headstock are at a disadvantage here.
Set centre height slightly ABOVE centre especially with large tool overhangs.
Wayne...
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wrote:

I'm sure Shakespeare was a machinist - hence "Parting is such sweet sorrow" ;-)
Regards, Tony
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wrote:

I thought that was Moses
-- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:- http://www.homeworkshop.org.uk /
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On Tue, 04 Apr 2006 07:30:49 GMT, John Stevenson

No, he was a footballer...Jesus saves, but Moses scores on the rebound ;-)
Regards, Tony
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Get a power hacksaw, or a bandsaw?
--
Charles Lamont

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