Source of Silver Steel

Due to a failure of the thread on the drawbar of my vertical mill I needed to source a supplier of Silver Steel in order to manufacture a replacement. I went online and found the supplier " Ground Flat Stock " and was surprised how reasonable their prices were. Their orders carry a £6.00 carriage charge so I decided to buy a number of different lengths to make it a viable order. As an example 7 MM by 333mm length was £0.96p plus the inevitable VAT. Another site I went to wanted more than three times as much for the same item. If anyone needs Silver Steel I would recommend that they check this website first, their web address is GROUNDFLATSTOCK.COM. They use UPS for deliveries so a reliable carrier. I stress that I have no connection with the supplier other than being a very satisfied customer. PS drawbar made and fitted, boy it's a tough job cutting a 3/8 whitworth thread in silver steel using a HSS Die.

Probably a little cheaper than Cromwells but throw the £6.00 on and it might be a close run thing.

Worth adding to my long list of bookmarks though

12mm Siver Steel isn't that expensive from Cromwell.

Recently I bought a 13" length of 1" dia from the local branch for about b£11 + VAT, if I recall.

If your Drawbar is longer than 13", they sell 1 metre lengths as well, so you'd have some left over for other jobs Used a 1 metere of 12mm the other year to fix a lawnmower in need of a new spindle (14" long!)

Howard

I have to ask why you made life difficult for yourself, plain good old fashioned mild steel would have been more than adequate for the drawbar. It is, at the end of the day, just a long bolt. If the thread on your old one failed I would venture to suggest that it is, or has been tightened far to much. Its only function is to prevent tooling dropping out of the spindle taper I also have a 3/8" whit drawbar, a length of 3/8" whit studding with a nut pinned to it and a 1" dia x 1/8" thick washer under the nut. Screw the drawbar into the tooling until it stops then give it a nip up with a spanner (no more than 1/8 turn) I have never had anything drop out using this method in well over 50yrs.

Mild steel will be fine.

Tony

Agree EN3 would have been good enough. If you want something better use EN8. Silver Steel is for making hardened cutting tools gauges etc, not shafts and axles. Rough guide, EN3 is now 070M20 the 20 means 0.2% carbon. EN8 is 080M40, 0.4% carbon. More carbon makes it stronger, but to get even stronger they don't add more carbon, they start adding other things, typically chromium, EN19 is 0.4% carbon 1.2% chromium. EN1A is low carbon free machining, not quite as strong as EN3 but machines like a dream. Silver Steel is ~1% carbon. If you want to weld it don't exceed 0.2% carbon or the heat affected zone can be brittle. If you really have to then preheat and controlled cooling are used

+1 - I have nowhere near Dusty's experience, but if I had to tighten a 3/8" mild steel drawbar anywhere near damaging the thread, I'd be looking for problems elsewhere.

Rob

I made a new M12 draw bar for my mill out of mild steel and it's been fine.

Why do they always seem to supply 3/8" whitworth draw bars? I've never used the one that came with my mill.

Not quite; the drawbar also needs to ensure that the taper is tight enough to allow it to transfer the motor torque to the cutter.

On my horizontal mill, which is INT40 with drive dogs, then agreed the drawbar is there only to stop the taper falling out. I would assume that a spindle with a shallow Morse taper doesn't need much tightening to transfer the drive torque. However, on a R8 spindle then the drawbar does need to be pretty tight to prevent the taper spinning under cutting loads. Been there, had that happen; and have had tools work their way out of the collets if not tight enough.

Having said that all my drawbars are low/medium carbon steel, although the CNC mill was transformed by making a silver steel washer to go between the drawbar and the top of the spindle.

Andrew

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IMHO silver steel is overkill. EN8 should be more than enough for the job.

Nick

Andrew, yes I agree, but my original statement is true. The drawbar has only one function. I did oversimplify that statement as it will, as you pointed out, require a bit more umph to hold a R8 than a morse taper as the former is not self locking. The point I was trying to make was that silver steel is probably not the best material for a drawbar.

Silver steel would not be my choice but if it were I would want to screwcut the thread.

Am I right in thinking that silver steel would wear better than mild or tool steel?

Prefer to find better uses for my silver steel !

In reply to those who questioned why the drawbar thread failed it was due to poor quality manufacture it was supplied with the mill. When supplied the thread was "rough" and due to the fact that only a couple of threads were engaging with tooling threads it failed mainly because of inadequate engagement. The replacement drawbar has had the length correctly calculated to ensure positive and adequate engagement and now works fine, silver steel was chosen for the replacement because I wanted the threaded portion to be hard to resist any damage from poor threads in tooling, I have found that the threads in a lot of the morse tapers on Chinese produced tooling are "rough" with torn and ragged thread forms, if we buy budget tools from China then we must expect varying quality so basically with the silver steel I am hedging my bets against the drawbar being ruined with use on poor threads.

Dave

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OK it was your choice and your money to do with what you wish.

I presume that you have hardened the threads after being cut with heat treatment though.?

Nick

Annealed silver steel isn't much harder than cold drawn EN8. Unless you have a captive drawbar I would screw the bar into the taper first, unloaded, then tighten the nut. That way the 'rough' threads in the taper are not rubbing under load.

Edited By duncan webster on 29/07/2017 12:23:02

Not yet hardened but on the todo list. Background in aircraft engineering so I do have tendency to over engineer my tools and models.

Dave

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OK so I presume you know what you are doing and 'over engineering' ain't a bad thing.

I am certainly far from being knowledgeable on heat treatment but I would think that a case could be argued that making it too hard could cause it to become brittle and liable to fracture especially if not of equal over the whole length as I imagine that could cause stress points. - But someone with far, far more knowledge than I have will be able to inform more.

Nick

In answer to Duncan yes it is a captive drawbar and length from shoulder is an important dimension and was wrong on the item supplied with the machine, just sloppy production. Problem now solved and a previous drawbar made from silver steel works very well so was the reason for material choice this time.

Dave

I remember reading an article by Tubal Cain where he explained why untreated silver steel was inferior to medium-carbon steels for uses subject to cycled loads. Can I find it?

Neil