Milling set up

I have a piece of BMS 6 by 30 by 100 long. I needed to reduce the width to 18mm. I wonder how others might approach this bearing in mind it's done on an SX2P, so not a big rigid mill. I've actually done the job to I think a reasonable accurate quality, but I wonder whether my approach was any where near right. I'll let you all know in due course how I did it, if I'm not going to embarass myself too greatly.

Regards

Martin

First I would scribe a line at 20mm and hacksaw offf the 1st unwanted 10., you can clean up the cut with a file if needed. I would then sit the job on a thin parallel in the milling vice such that the remaining 2mm or so can be machined off the sawn edge.

Maybe take 6mm off either side to stop it bending?

Guaranteed that if you only mill off one side it will bend due to the stresses induced by the milling.

Do as Tony says but instead of taking off the full two mm, rotate after one mm and reduce the other side by the remainder.

Lofty

In my understanding, milling one side tends to reduce the stress, as the harder surface is removed. This leads to the stress remaining the other side taking over.

In the recent spirit of unhelpful answers, I would pop down the road to the local steel fabricators and see if they had something nearer the size to start with.

Cheers,Tim

Too long for my bandsaw and I'm too lazy to hacksaw that much by hand.

Easy way for me would be to put it in my milling vice and cut down 6mm with the base of a 4-flute end-mill . (Turning over to do the other side.)

Actually, to preserve the precious end of the cutter, I'd go the extra mile by removing the vice and clamping the work direct to the table with packing underneath so I could use the rarely used upper part of the flutes to cut the 6mm edge sideways.

I normally use a 10mm carbide end-mill flat out for bulk work like this - no lubrication, and hacking as much metal off as the machine will do without complaining. It gets HOT! If the finish demands it, I switch to HSS plus lubrication to do the final cuts. If HSS is used to remove a lot of metal, I flood cool.

Dave

Just as pilots say that any landing you can walk away from is a good landing, so any way of cutting your flat that gets the result you want is fine.

I think I'd probably saw off about 10mm from the width with a jig saw, clean up the cut in the vertical slide on the lathe (I don't have a mill - yet), and if I noticed any bend turn it over and mill the other side down to size. Although aware of the risk, I've seen quite a few cases where such bending doesn't actually happen, or is inconsiderable if it does.

To stop the issues of distortion I automatically normalise bms before machining. Easy to do, heat to red hold for a couple of minutes and cool slowly, I usually cover with a couple of fire blocks to slow the cooling. You can then saw the excess of either side and skim in the mill to size.

You could have bought 3/4 x 1/4(19.05 x 6.35) and not worn your cutters out so much.

Michael

Interesting, several answers all with valid bits in. The reason I'm asking is that I'm doing Steve Jordan's mod on the lathe saddle so I phoned a local steel stockholder as to whether they had any bar ends 6 by 20 and 5 by 30. As it was the best they could do was 400mm of 6 by 30, for a very small sum. The only critical dimension is the 6 one so I decided to mill the 30 down to 18. Like silly old duffer I'm far too lazy to want to hacksaw it and whilst I could of got the jig saw out but didn't think of it. The biggest cutter I have is a 12mm 4 flute so I just persevered, it took forever, the mill is not rigid enough to take hacking great lumps off in one go.There is no sign distortion by unbalanced stresses but then I wasn't going hard

Anyway it's ended upwhere I wanted it and whilst I acknowledge that cutter usage was far greater than it might otherwise have been it was only a cheapo, so all in all even If I have to replace the cutter the whole job will cost less than £20.

Thanks for all the thoughts, I would do it differently next time.

Regards

Martin

Edited By Martin Shaw 1 on 07/01/2018 18:38:08

My local stockholder would have done you a full 3m bar 1/4" x 3/4" or 6x20mm BMS for lots less than £20.

Neil

Neil

Martin's cutter might have been £19

I think I would have cut the strip off by hacksaw. About two minutes' work at most. It's only a 100mm cut in 6mm plate. Then one finish cut in the mill and it's good to go. I have never seen flat bar bend significantly when machining off one side on the "long" side like this. Takes a bit of force to bend steel 18mm thick. If you were machining the "short" side down from say 6mm to 4mm you might be more likely to experience bending if only one side were machined.

We used to demonstrate this to apprentices.

Take a piece of BMS 150mm x 40mm x 30mm and reduce the 30mm to 20mm using a 60mm face mill on a R8 Bridgeport.

Each apprentice would be given the opportunity to remove the whole 10mm in 1mm cuts or a 5+5 with a turnover.

The single sided cut always ended up with a .005" ish bow in the middle when checked on a surface table.

Just to demonstrate a point to them.

Lofty

Neil

Yes of course the steel itself wouldn't cost that, the sum of £20 includes studs, washers, nyloc nuts, the piece of steel itself, and a replacement 12mm cutter. As it is I probably don't need a new cutter so take £7 off. If I had been prepared to purchase full lengths I would have got them at an exact or nearly so size, but I would have ended up with 5m of steel bar lying around which I may or may not use. As it is I have got what I wanted for the minmum cash layout, albeit at a trade off of time, and no surplus material. If I had thought better to hacksaw the majority off and make a few passes on the mill to finish it would have been quicker, I'll know better next time. Thanks for everyones input, its been useful.

Regards

Martin

Edited By Martin Shaw 1 on 08/01/2018 14:39:35

To add confusion, and make a big drama out of the job; my method would be:

Hacksaw to a little over 100 mm length (You did say that you had a 400mm length?)

Clean up the sawn ends, and bring to 100 mm long. This will employ the less often used flutes of the end mill.

Set the metal in the vice so that the 6 mm thickness is held in the milling vice. (30mm face vertical)

Using a slitting saw, remove 5 mm from one side.

Turn over and remove 5mm from the other side.

Change to an end mill and clean up the just sawn surface.

Turn over and mill the other side down to produce the required 18mm.

Hopefully, any bowing due to stress relief will not affect the finished product.

And one day, you may find a use for two bits of metal 100 mm x 6 mm x 3 mm!

Howard