Making half-round steel pieces

[AdeV]

I need to make/buy some 4" diameter half-round steel bar pieces each 3.5" long. Unfortunately, no-one seems to stock anything bigger than 3", and even 2" is £lots/foot.

So... making...

What's the best way in your opinion?

1/ Buy 2x lumps of 4.something * 2.something * say 4" steel. Glue together. Turn to size in the lathe, chop square end off.

2/ Buy as above, but mill each one in the milling machine, either on the rotary table (manual) or CNC.
(optional step 2a/ When close to tolerance, glue together and finish in lathe for perfect circularity & finish

3/ Buy slightly larger (4.125" say) diameter round bar, cut to length, beg Mr Mawson to cut them in half with his EDM wire cutter, then finish in the lathe as per step 2a.

4/ Buy my own EDM wire cutter and proceed as per 3, only without the begging (hint: this one isn't practical)

5/ Something else I hadn't thought of.

All comments welcomed!

[awemawson]

Buy 4" bar and slice it in half with a band saw thus saving at least 20 hours edm time 

[Lew_Merrick_PE]

Ade,

Not knowing your shop or tooling...  Here in the U.S. (moderately) large diameter steel round bar normally comes in ø4 (±.016), ø4.25, ø4.50, etc. types of diameters.  Now, assuming that you have a steel-cutting bandsaw, a somewhat greater than ø4 inch diameter should be easily cut into (2) something greater than ø4 inch pieces.  Dress the faces and bond together using (say) acrylic adhesive (with, maybe, some screws & dowels in "excess length") and turn to size.  Cut & dress to length.

The reason I am suggesting acrylic adhesive is that a moderate stint in a -5°C freezer will made the bond brittle enough to break with a BFH and a solid support.

Would that work for you?  [Irrational minds want to know...]

[AdeV]

Unfortunately, my bandsaw is more of a woodworking bandsaw than a metal one, it runs way too fast & blunts blades in no time if you get them to cut anything harder than, well, wood. Even aluminium kills the blades off. Plus, the blade tends to wander, even if I try to use a fence it starts trying to cut either closer or further away, and once it's off course, there's no bringing it back.

So... bandsaws, unless someone's got a really good one they'd be prepared to cut a few bits of steel for me, are not an option.

BTW, I need at least 4 of these things, so that's a little over 7" of bar to cut up.

Lew - will acrylic glue survive the heat of  machining? I'd assumed the use of cyanoacrylate (superglue), allowing plenty of time to cool the bar after taking a cut.

[AdeV]

Hmmm.... I could use a circular saw in the mill.... I'd need to go for at least 4 1/2" OD due to the thickness of the cut, but it'd still be less deadly than trying to round off a 4" square section, I reckon.

[vtsteam]

I'd probably go with option #1, except maybe I'd tack weld them at the ends, and grind those off after turning.

I'd also probably  turn between centers, so center drill first, and maybe even weld a temporary bit of rod as a dog on the end to engage the plate slot

After that I'd rough off the outside corners with a hand grinder to approximately 8-side it before mounting for final turning.

I don't think it would take long to turn something that small which was already roughed out.

[shipto]

Is the aim here to end up with something like 4 really oversized woodruff keys? I would probably get 2 bits of 2 1/4" by 4 1/4 bits then face them off to fit nicely together and either bolt or weld them at each end before turning them to round and seperating them which I think is your no1 suggestion.
Sounds by far the quickest and most cost effective solution to me.

[mattinker]

How about having them flame cut from  3 1/2 plate?

Regards, Matthew

[Lew_Merrick_PE]

Lew - will acrylic glue survive the heat of  machining? I'd assumed the use of cyanoacrylate (superglue), allowing plenty of time to cool the bar after taking a cut.

Yes, CA adhesives will survive up to (about) 450°F, but they are brittle and shock adverse.  Acrylic adhesives are only good up to (about) 230°F, but they are much less sensitive to shock loads.  This is why I also recommended making the entire piece longer and installing screws and dowel pins.

[AdeV]

For those wondering what it is I'm making... I'm copying the vice jaws of a Manchester Rapidor hacksaw for a couple of guys on another forum. The half rounds are 3 1/2" tall, and rotate within a backstop, and allow you to set the saw to cut at +/- 45 degrees from "straight ahead". They're held in place by a single large bolt, there's a curved slot cut in them which allows them to be rotated.

You can probably see what I'm making in this picture, courtesy of the mig-welding.co.uk forum:



Obviously, the originals were cast, presumably the front faced to give a smooth surface, then they'd be glued(?) together and the outer diameters turned to size.

[DavidA]

Ade,

Just get your supplier to cut a length off the stock and then ask a local engineering firm to slice it down the middle with a band saw.

The company I worked for had a parallel bandsaw that would cut up to a foot thick with ease.
On the usual 'pivoted at one end ' saws we cut pipes up to 24 inch diameter on a regular basis. The trick is to keep the blade feed rate down so it doesn't wander off.

John Wilson (steel), Keighley will supply and cut the stuff a you want it.

Dave.

p.s.
It may be cheaper to buy 4" bar and then split it off-centre. Then cut the slightly more than half diameter  sections to length and mill to exact 1/2 diameter .
You will,  of course, need twice the length using this meth0d. But it may be cheaper than buying over size bar.

[Lew_Merrick_PE]

Ade,

You do not need a perfect half cylinder for your vise.  So long as the two pieces are (reasonably close to being) the same thickness from the pivot face, it will work just fine.  If you cannot cut the ø4 inch bar accurately with your (existing) power hacksaw, then there is almost certainly somebody within a reasonable distance who can cut it for you.  Then it is only a case of mounting the two pieces together with an appropriate shim using screws and dowels (or roll pins) in the excess, turning the OD as required, and cutting to actual length.  ???

[shipto]

ok now i know what your making I have a suggestion. What about taking a bit of 4" X 3.5" X 3/8" plate a bit of 3" thick wall tube and a bit of 4" thick wall tube and arrange them as in the pic. You could fill the gap in the smaller tube then machine it all to make it pretty.