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Steel for machining

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Adam Harris04/10/2018 14:22:49
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I want to get a steel billet for machining into an overhead support arm for a horizontal milling machine. It requires me milling dovetails for sliding on a dovetail joint. Could anyone tell me the spec of steel I should be ordering from the stockholder? Thanks

Neil Wyatt04/10/2018 14:32:55
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If it won't be moved a lot and won't be welded EN1A Pb is affordable and probably going to make the whole exercise less stressful.

Andrew Johnston04/10/2018 14:41:40
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Not really enough information to make a sensible choice. Are you talking about the overhead ram or the outer arbor support that hangs on the ram? And what rough size?

If we assume that the steel lump is going to be fairly chunky it'll depend on what you can get rather than what you want. For an overhead ram I'd use hot rolled steel. It'll be cheaper than cold drawn and won't resemble a banana when you try and machine it. For an arbor support again I'd use hot rolled steel for the same reason. Or you could use continuously extruded cast iron as, again, it won't distort much when machined. Most original arbor supports would have been iron castings as were rams, unless round supports were used.

Andrew

Adam Harris04/10/2018 15:43:09
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Overhead ram / arm sliding on a dovetail joint to support end of horizontal milling arbor

JasonB04/10/2018 16:08:53
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I think I would go with Andrews suggestion of cast Iron bar as it is easy to machine and unlikely to move though to be safe I would rough out then let it rest for a couple of weeks before finish machining.

You can easily get hold of Grade 250 (old GR17) cast iron bar in square or rectangular section cut to length.

Adam Harris04/10/2018 16:24:42
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How easy is it to machine a smooth sliding surface on cast iron with a milling cutter rather than a surface grinder??

David George 104/10/2018 16:39:42
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Hi Adam. Machining cast iron is if anything easier to get a nice sliding finish on that sort of item as that is what was used on the majority of that sort of item, but you would be using a solid piece of material, unless you commissioned a casting. The drawback to cast iron is it is a dirty material to machine and produces a lot of graphite dust but that is why it makes a nice sliding item and it is fairly stable when roughed out and left to stand for a few weeks outside in the weather. What sort of size mill is it for and have you got any sizes as that would make all the difference to the type of material you would use as a heavy solid piece of steel may sag or bow the original machine.

David

Andrew Johnston04/10/2018 16:57:06
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Posted by Adam Harris on 04/10/2018 15:43:09:

Overhead ram / arm sliding on a dovetail joint to support end of horizontal milling arbor

Unless I've misunderstood that's going to end up as an L-shaped item? So that's a huge amount of metal to be shifted if the mill is of any reasonable size. It would be way better to make it as two separate parts.

Andrew

Adam Harris04/10/2018 16:57:19
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It is a small affair for a small Aciera F3 - finished article requires starting with a min billet size 21" long x 5" wide x 6" tall. The overhang required is only 7" and since I only have one arbor it is not likely to require greater overhang (small table) nor indeed variation in position on slide, but it is an accurate mill deserving of a nice stable arbor support!

Adam Harris04/10/2018 17:00:47
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No Andrew it will be made as one part as per the original.

HOWARDT04/10/2018 17:00:53
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If you are are talking of an arbor support bracket, then I would go with a flamecut blank. Steel specification is not critical but you may find 080M40 (EN8) and 080A52 (EN43) as being most common. Cast iron Grade 250 can be expensive in big sizes.

JasonB04/10/2018 17:16:06
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Looks L shaped to me as Andrew says?

Which is a big chunk of waste material to take out of the block. Would be easier to make the ram in one piece and have a separate end that could be doweled and bolted on, even fill theholes so they won't show when painted.

Dave Halford04/10/2018 17:21:41
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Centec style arm makes more sense unless you have the casting

Andrew Johnston04/10/2018 17:23:06
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Posted by Adam Harris on 04/10/2018 17:00:47:

No Andrew it will be made as one part as per the original.

Yes, but the original would have started off as a casting, not hogged from a solid lump. For a start a blank that size is going to weigh about 250lbs. Don't know about you, but that's way more than I can lift. Looking at M-Machine-Metals they don't do a cast iron rectangle that size, but you could get 200mm diameter round, which will cost you £588+VAT for 21".

Andrew

Adam Harris04/10/2018 17:23:24
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Thanks for the interest/advice but it will be made in one piece with yes a lot of material removal - could kind responders please return focus if possible to my enquiry as to best material (steel spec) to use ?

not done it yet04/10/2018 17:29:54
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I think I would be making the dovetail from flat and simply affixing a beam above - which could even be a lump of RSJ and be perfectly serviceablesmiley. But machined from one piece would not be too difficult. Pivoted at the rear and positioned carefully, with a fixing from above at the front, for alignment would be straight forward.

Making a small sliding (on the dovetail) arbor support bearing would be a separate piece.

Nothing fancy but adequate. There are many riser blocks out there, made for Centec mills, in aluminium. Even a second hand horizontal arm from a Centec could be purchased and remachined, if of sufficient size.

I most certainly would not be making that whole item from one piece.

Edit: Dave Halford got to it long before me.  Sorry, but rediculous to make it from one lump, IMO.

Edited By not done it yet on 04/10/2018 17:32:27

SillyOldDuffer04/10/2018 17:33:23
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Posted by Adam Harris on 04/10/2018 16:57:19:

It is a small affair for a small Aciera F3 - finished article requires starting with a min billet size 21" long x 5" wide x 6" tall.

...

Might be a small affair for you Adam, but a billet that size will weigh about 90kg (200lbs). Too much for me to lift even when I was young and fit. (As for lifting it today, youth, beauty and physical fitness all deserted me back when we still had £sd.)

Do you know what load the bracket is expected to take? Might indicate something high-tensile is needed. Also, if the load puts the finished bracket in tension it might not be a good idea to use cast iron, though I confess I don't know what that part of a horizontal mill is normally made of and could be talking rubbish.

How much wear and tear expected on the dovetails? Mild steel may be a bit soft, although it could be case hardened.

Tasty project - good luck with it.

Dave

Edit: apologies, I see others have made the same point about weight.  I must learn to type faster.

 

Edited By SillyOldDuffer on 04/10/2018 17:35:25

JasonB04/10/2018 17:56:47
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I suppose if you went the flame cut steel plate route it would be worth getting it cut to the basic L shape, what you would pay for the extra cutting would be worth it in time and cutter wear costs. So as said EN8.

That would also bring it down from 77kg to about 50kg and as you would need to lift the finished item anyway a few more KG still to come off won't hurt

Andrew Johnston04/10/2018 18:07:58
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The original would have almost certainly been cast iron, not steel.

Andrew

JasonB04/10/2018 18:20:35
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Yes agree with that Andrew and I would say the nicer of the two materials to machine. Solid 150 x 150 square bar would be the nearest available. handy if the supplier could saw or otherwise cut it down to a basic shape.

Would have thought a scraped finish more appropriate then grinding on a machine of that quality and CI scrapes well. Though the arm only moves when being fitted so a good machined surface would probably be OK.

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