making spacers from one piece of steel

I need 2 spacers, 9cm outside diam 1.5cm thick with a 5cm diam centre hole, and 2spacers 4.5cm od, 1.5cm thick with a 1.5cm centre hole. I have a piece of round steel bar 10cm od and 4.0cm thick. Can I use this one piece of steel to make all four spacers and if so,how ? or do I need to get some more steel. I have a 9" South Bend. Thankyou

look up "trepanning".

Followed by "parting off"

As that is likely to give more trouble than boring/trepanning out the hole at 100mm dia

Edited By JasonB on 21/07/2015 13:00:41

I would just make the smaller bore ones first parting the 2 off and then the larger ones finally parting each off. I don't think I would bother trepaning the 45mm out just turn the 100mm to the right size for a distance a bit over twice the spacer thickness plus twice the parting off tool thickness. After all it is a southbend, it wont take long to get down to 45mm dia from 100.

Making and parting off the smaller ones first means that the depth of hole drilled and bored wont matter.

The problem people usually have parting off is going too gently / slides too loose / tool blunt / above centre / loose headstock bearings. Some sense has to be used in respect to too gently but often if the rest of the lathe is ok speeding up the feed a touch will get rid of the horrible chattering noise that some times happens. If it doesn't it's a case of carrying on. If for one reason or the other there are chatter marks on one face on jobs like this make them a bit thicker, grip on the outside of the 3 jaw jaws and face them. If the lathe is normally noisy parting off better finish will usually be obtained facing from the centre out and in other cases too. Sometimes with the cutting edge of the tool only at a slight angle to the work - this increases the size of the cut even when fine ones are taken - bigger cuts take more of the play in the machine out.

On a southbend the most probably cause of any problems will be the headstock bearings if the slides are slightly on the tight side. Unlike a Myford of rear parting off fame to try and get round it the lathe's bed is very unlikely to have anything to do with it..

John

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Roger only has 4 cm (Length.) of the bar so he could only get two 1.5 cm slices from it.. I do not think it is possible to trepan through 1.5 cm to give a hole of 5 cm dia. and to leave the cut out 4.5 cm dia. Even without allowing any clearance the tool would only be 0.25mm thick.

Les.

0.25cm surely ie 2.5mm? Even so, barely enough.

You should just get some length of 2" round and be done for the smaller ones. There's 5mm length left for facing off and parting the bigger ones. 2 cm parting depth required, so as John says, don't mess about - go big or go home! Use coolant if you can.

Murray

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Holesaw mounted in the chuck.?

But if you have not hot one of the right size the blade and the arbor of a decent maker would cost far much more than an extra piece of steel.

Nick

Hi Murray.
You are right. I can't claim it was a typing error as I was visualising a 0.25mm thick tool. But as you say even 2,5mm would be very weak if it was long enough to get though 1.5 cm. He could do it if he bought a wire EDM machine.

Les.

Two things occur to me the thickness of the spacers will probably preclude getting enough safe grip to part off the second spacer. Mathematically you can get 2 out of his 40mm length, but in reality this is unlikely. So the answer to the original questions are...... NO, and you need a longer single length of steel, or 2 longer lengths of different diameter.

The second thing is I am stunned at the reluctance to simply suggest parting off the spacers after drilling or boring the centre hole. The wall thicknesses are not great. Hole saws?Trepanning? Utter nonsense. The overhang on the parting tool will only be 20mm and 15mm.

Can't see the point in parting off the second spacer, just face it where you parted the first and then flip it over and face down to the finished 15mm. One parting cut mid way along teh 40mm length is all that is needed.

Mike the reason for trepanning/holesaw was to try and save the lug out of the middle to make the 45mm dia spacers which is what teh OP wanted to do. If the blanks were faces to 15mm thickness first and then trapanned in from either side thats only 7.5mm overhand but still a bit tight if you wanted to clean up the cuts

Edited By JasonB on 21/07/2015 16:46:40

> Two things occur to me the thickness of the spacers will probably preclude getting enough safe grip to part off the second spacer.

Not if he holds the spacer in the chuck (15mm thick) and parts or faces off the waste.

I don't know why he can't do it with a fretsaw

Neil

I thought that was precisely my suggestion. Of course, 20mm will still be too much overhang for some here but that's another matter....

I wouldn't use a fretsaw myself, mainly because I don't possess one.

I would take this challenge as a prompt to go out and stock up on steel. Clearly the stock levels have been allowed to diminish beyond an acceptable minimum! As Noddy used to say, it's better to have too much than not enough.

Murray

2.5mm too weak for parting off ?????????

Words fail me especially as i often use a blade 1/16 thick. The thickest one I ever use is 3/32 thick

One thing I forgot to mention about parting off that will cause problems. The blade must be square to the axis of the lathe. I do that by using the face of the chuck that is holding the work.

I am assuming that the OP does have a parting off tool because grinding one from a tool bit to go to a depth of 20mm wont be easy but could be done but I would be looking for some 5/8 thick tool bits ideally or 1/2in - the same depth as fit in Myford sized parting off blade holders. Actually Southbend tooling is likely to be deeper. My Boxford sadly has a Myford branded tool post on it. They fit the same holders as on their other lathes even though there is more height available.

John

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Edited By John W1 on 21/07/2015 22:51:04

One thing I missed on this is the 100mm dia bar, maybe because cms were used. That's too big for the chucks that normally come with a southbend. The best bet for holding it would be the 4 jaw with the jaws reversed but even that is a bit risky without more support. The 4 jaw will hold work far more securely than the 3 jaw.

The best way to do it would be to use the fixed steady. Chuck the work, set the steady and face and centre drill the end. Remove the steady fit the centre and skim up the work right back to the chuck, just a light cut. Set the steady again, it now has a surface that is running true, leaving enough space to make the 2 smaller ones. Drill and bore, turn the od and part them off. Same with the larger ones but you will finish up with the steady rather close to the chuck. Maybe closer than it can get, you'll have to check. In that case you should be ok parting off the last one without the steady as the projection will be low.

When mounting it in the 4 jaw adjust the jaws to get it running as near true as you can not forgetting to tap the far end to get that running as true as the part in the chuck. Final adjustment if needed to get something very true is done while fully tightening the chuck. If that doesn't work out go back to adjusting the jaws. It takes a bit of practice.

I might have ordered up suitable slices of material but if the faces needed to be rather parallel an expanding mandrel would have to be made as well. Not easy with bores this large.

LOL this assumes that the bar is long enough of course which unless the measurements are messed up it isn't even if no material is wasted making them, 4 x15mm = 60mm which is > 40mm It's probably big enough to make 1 without any parting off unless the faces need to be parallel. The o/d could be turned by doing half and then reversing the work in the chuck and doing the other half, Bore and then part off and finish the thicknesses individually. They faces could be trued up to the bore and made parallel but that would need an expanding mandrel - easy to make for small bores but not for ones of this size.

John

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That was a comment about a trepaning tool not a parting tool

Hi Roger,

It is possible to make the 4 spacers from a piece of steel only 40mm thick but would need a special tool to cut the 2.5mm groove. A hole saw as suggested, could be used (if you have one for this diameter) but would leave a rough surface which would have to be cleaned up.
It would be much easier to buy some more steel. Possibly hollow bar for the large spacer. Or have it profile cut from plate and machine to finished size. Should not be too expensive and much easier to make the spacers.

Paul.

Sorry. I don't really see trepaning as an option so thought that had gone out of the window.

In principle the work could be done with a trepaning tool under 2.5mm thick or via a change of sizes but it would need some rather careful grinding to avoid weakening it too much - the same order of precision ground into parting off tools, rather shallow angles. The side facing the inner diameter can be square to the top. The angle needed on the side facing the outer diameter depends on that diameter. The tool would finishes up like a narrower version of this

It's not a lot different to parting off really so in principle ground correctly a 1/2in HSS tool bit should be able to do it. 2.5mm might be ok if the clearance needed on one side doesn't neck it in too much This one was ground to work on diameters larger than something around an inch and a similar tool has been used for trepaning but not after a particular core diameter. The in feed it can handle in one go is small due to the width and machine power so it was used to face an area away that gets smaller as the cut deepens.. This one is 5/16 HSS. I use it for boring shallow parts. The only time I have trepaned with a tool like this was on a Peatol. No chance of drilling a decent sized hole to bore out. A very large washer around 5/16" thick, 4" dia and 2" or so bore.

John

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I think this is just too much like hard work, far better to buy a piece of 2" steel bar and machine the smaller spacers from that. I never quite understand why some people try something that is really not worth all the effort KISS.

Bob

I think it could be done, first take the OD down to 90 mm, then split the bar in half, and face to 15 mm thick, then here's the tricky bit, trepane the centre out by going in half way then turning the disc around, then going in the other half. Sometimes I try these ideas out, sorry not with this one.

Ian S C

Cm ?????????????

Only the BBC and dressmakers use Cm, engineers use mm, real engineers use metres.