Horizontal mill cutter runout

[JasonBModerator @jasonb]

There are quite a few small mills with this sort of lever feed, friend of mine has a Sixis 101 where they are on all axis. They were used for all sorts of things where a quick or repetitive action was needed much like a capstan or cut off slide on a lathe rather than general feeding. But generally for lighter cuts in non-ferrous materials.

Say you want to cut a hexagon on the end of a part. Fit a rapid indexer on the table and adjust so that each face can be cut in one pass. It is then just a two lever job to cut-spin the indexer-cut- spin etc. So ideal for small batches but if doing individual cuts then you would use the handwheels.

 

Your backgear speeds sound more usable for the cutters you have. What is the tooth count and width? Should be able to work out a feed from that which will keep all teeth doing something.

Eg if we said 100rpm and it is a 30T cutter then 0.002″ chipload per tooth will be more than the 0.001″ runout then that is a feed of 0.060″ per rev or 6″ per min. Assuming the leadscrew is 10tpi then should be quite possible to wind at that rate which is one turn per second.

[BazParticipant @baz89810]

Obviously an awful lot of you have never worked in a machine shop, if you had you would have seen small horizontal mills doing second op work, putting slots in various components, operated mainly by women. The machine would be run flat out with a slitting saw, maybe two or three of them on the arbor, the work being held in a fixture on the table, maybe many components being done at once, lever feed was used because it was quick, time is money. Nobody gave a toss how true the arbor was running, how true the cutter was, it may even have had a couple of teeth missing, it didn’t matter, the job was done and it passed inspection.

[duncan webster 1Participant @duncanwebster1]

I was once given a small horizontal milling machine that didn’t have a screw feed to the x direction, only a lever. I passed it on to someone else, not much use for model making.

Surely what matters is the difference between the cut on adjacent teeth. One thou across many teeth will be a lot less than the chip thickness, so won’t matter.

[BazParticipant @baz89810]

Absolutely right Duncan. Take a 4 inch slitting saw as an example with perhaps 60 teeth, if the tooth load is 0.002 per tooth that’s 0.120 per rev, about one turn of the handle per rev,  now let’s run at 350 revs and you will see why you need a lever, out will never wind a handle quick enough. As you say lever feeds are not much use for model engineering.

[Mick BaileyParticipant @mickbailey28509]

Here’s the full speed range for the machine, which makes it quite versatile along with the vertical head. The principal issue is as I’ve said before  – the torsional reaction in the rapid feed cross shaft and under heavier cuts, slippage of the clamping mechanism. The cutter currently mounted is a new Firth 5/16″ x 4″ 16 tooth cutter. I’m using this on mild steel.

Helical slab mills operate a lot better due to the shearing action and constant tooth contact.

Maybe the cross shaft and clamp would be better cleaned of lubricant for use in the locked (handwheel) position to afford a better grip.

It really would be interesting to see the original user manual for the standard machine with its high spindle speeds. Clearly there was enough of a shortcoming that it was worthwhile redesigning the drive arrangement.

 

[JasonBModerator @jasonb]

Well a 16T cutter should be easy enough to feed by hand.

Taking the 0.002″ that I mentioned earler that is 1/32″ feed per rev. @70rpm that is just over 2″ per min = 1 turn ever 3seconds and @100rpm 3″ per min 1 turn every 2 seconds. Even if you doubled the chip load to 0.004″ it is quite epossible to wind at those rates. leave the eapid lever alone.

Whether the machine is upto driving the 5/16″ wide cutter is another matter, gearing should give the motor the advantage it will be the rigidity that determines what can be removed.

[Mick Bailey]

On Mick Bailey Said:

[…] It really would be interesting to see the original user manual for the standard machine with its high spindle speeds. […]

That ^^^ is an extremely good point, Mick … and is probably more widely relevant as ex-industrial machines continue to come into the hobbyist’s reach.

MichaelG.

[Mick BaileyParticipant @mickbailey28509]

I’ve now got the machine operating as I was hoping for. With the aforementioned cutter it has no trouble at all in removing metal at a decent rate and leaves a nice accurate finish in mild steel.

The biggest problem has been the slippage of the rapid feed spindle lock. Ther isn’t a great deal of clamping force to hold the shaft and it was well-lubricated. I chose not to dismantle the mechanism, but gave it a good clean with a can of brake cleaner. I’ll lubricate it when I come to use the rapid feed. It now holds far better, though the torsional rigidity needs improving.

A second problem was the material I’d been milling. I took it from my mild steel offcut stock, but I now realise it’s something far tougher and a real challenge to cut. I only found out when I came to hacksaw a piece off to reduce the length. After swapping this out for some verified mild steel there was an instant improvement.

 

[Mick BaileyParticipant @mickbailey28509]

After some machining this morning the clamp started slipping again, reducing the ability to feed quickly enough with a decent depth of cut. I thought that the machine wouldn’t have come out of the factory like this and investigated further. The rapid feed spindle is locked by a threaded cross shaft that carries two clamps, each one having a semicircular cutout that’s supposed to grip the spindle. Those cutouts are a rather poor fit on the spindle with very little contact area due to a mismatch in radius. They’re burnished due to slippage, though everything appears to be factory original.

I can’t see how this would ever have been a satisfactory arrangement. It looks to be a straightforward machining and fitting  job to improve this considerably without having to redesign the mechanism.

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