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EN1A verses black mild steel.

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old mart26/08/2021 20:27:26
3347 forum posts
208 photos

I am looking at making some replica helicopter blade bolts which will be tapered and threaded each end. I require 1 metre of 22mm diameter steel. My first choice is ENIA for its general machinability. While looking, I noticed that black mild steel is cheaper, but the sellers do not mention the grade. I suspect that the black stuff might not be so nice to machine, any thoughts on the subject would be welcome.

JasonB26/08/2021 20:39:09
21451 forum posts
2453 photos
1 articles

If it's not mentioned then it may not be so nice though you can get black EN1A but EN3 is more usual. You may also have to buy one size up if you want 22mm finish as you will have to machine the surface off the black bar and that may put the cost up a little.

Edited By JasonB on 26/08/2021 20:47:28

old mart26/08/2021 21:02:32
3347 forum posts
208 photos

The 22mm diameter is perfect as the largest diameter will be in the region of 20, and also because the spindle bore of the Smart & Brown model A is 63/64", about 25mm.

I was thinking that the black might be EN3, and that would make the saving in price not worth while.


Brian H26/08/2021 22:19:14
2230 forum posts
113 photos

I assume that the bolts will be used for static display of a helicoptor and not a flying one!


Robert Butler26/08/2021 22:27:29
291 forum posts
6 photos

Unusual for 'bolts' to be threaded both ends? Studs perhaps?

Robert Butler

peak426/08/2021 23:19:58
1499 forum posts
162 photos

Old Mart, I guess it depends on where you live, but surely the difference in cost is fairly marginal.
The last 1" EN1a I bought, and collected personally, was £5.50 per meter; I appreciate steel's gone up in price, and that was about a year ago.

Clive Foster27/08/2021 09:11:35
2837 forum posts
103 photos

These days I'm awfully chary about buying anything that doesn't have a proper, modern, BS970 1991 designation. Preferably with a T on the back for condition.

EN numbers are way beyond obsolete these days and all too often whats on offer as "equivalent" is more or less dregs at the bottom of the barrel stuff that sort of, more or less, crosses the specification somewhere. Especially in these days of COVID et al supply difficulties. EN numbers often seem to be considered the province of unsophisticated users doing simple things for which something close will do. Basic fabrication and the like.

If I'm going to the trouble of machining a part I can do without struggling with material that doesn't want to play ball. Generally not an issue for me as I have industrial weight machines so turning on the coolant and leaning on the cut usually sorts it. Can do without wiping out an insert edge or having to resharpen my "standard" HSS tool though. Not t mention taking an hour for a five minute job.

Different story for folks with lighter machines.

I'm convinced one length of "mild steel" that was passed to me as "blowed if I can machine this stuff" was actually rebar! Binned!


Graham Meek27/08/2021 11:15:02
398 forum posts
259 photos

Machining EN1A is like using a hot knife going through butter, in other words dead easy. Machining Black bar I have likened to trying to machine a Brillo Pad, or Wire Wool.

Money saved in the initial purchase will be wasted on electricity trying to get a good finish. That goes without the cost on ones patience during the machining process.

Is this material grade correct to the specification for this application?



old mart27/08/2021 13:05:11
3347 forum posts
208 photos

The blade bolts are for a Piasecki H21 flying banana twin rotor with six blades. We only have about 3 blade remnants, so 6 bolts will be plenty. The bolts are slightly larger than a Wessex bolt and from the limited pictures are similar desigh with a thread either end. On the Wessex the tapered bolts are pulled tight by a nut with a large flange, which also fits the other end. When removing or loosening a bolt, the nut is fitted to the large end to break the taper. We don't have any Piasecki nuts, but Wessex ones are the right size and have 1/2" UNF threads and most importantly readily available which will save me making them from 38mm bar.

Original bolts would have been made from heat treated chrome moly, but mild steel is plenty for a museum exhibit.

Edited By old mart on 27/08/2021 13:08:05

Brian H27/08/2021 15:01:37
2230 forum posts
113 photos

Sounds like an interesting project. Could you say where this project is taking shape?


Mark Rand27/08/2021 16:22:19
1061 forum posts
12 photos

A very specific issue with leaded EN1A alloys is that they'll rust if you even look askance at them. So don't use them where they will be in the open for any great length of time without protection (even indoors).

old mart27/08/2021 16:40:13
3347 forum posts
208 photos

The Helicopter Museum is at Weston-Super-Mare, in the UK. I got bored and just ordered a metre of the 22mm EN1A from the cheapest ebay seller today, just over £24 post paid.

The threading will have to be done before the tapering, there will be no parallel surface to hold onto after the taper is produced. The easy way for me will be to turn a couple of inches of 1" bar true and put a 1/2 UNF female thread in it. Then each blank with the threads either end and one centre for tailstock support can be screwed into the chucked up holder for taper turning. The Smart & Brown model A has the taper turning attachment, which makes it easy, as the length of taper required is twice the compounds movement.

Edited By old mart on 27/08/2021 16:41:47

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