High Speed Milling

[JasonBModerator @jasonb]

One other thought that is used a lot n CNC is to machine the part from thicker stock so you have something to hold in the vice and then run a saw down each side to almost separate the part from the remaining stock, done right you get a foil thickness if material left which stops the part being lost in the swarf;

[John HinkleyParticipant @johnhinkley26699]

Coming in a bit late on this subject and with zero experience with either horology or high speed milling, I offer the following:

It seems to me that it might be feasible to use a larger cutter, as suggested by Jason earlier, and "sandwich" the workpiece between two sacrificial pieces of, for example, brass, milling away all three pieces of material at the same time. No need to go completely through the lower slice. Use the hole to secure the slices together and/or secure to the work table, with or without superglue assistance.

John

Jason's link appeared while I was typing!

Edited By John Hinkley on 10/07/2023 13:06:53

[Iain DownsParticipant @iaindowns78295]

Well, I'm getting a bit closer to my objective (though no longer 'high speed milling&#39.

The latest attempt used an HSS 2 flute 4mm cutter at 2200 rpm, superglue, but this time to a flat fixture (no grooves) and a lighter DOC (0.10 / 0.15mm).

The result is this

The thickness has gone quite well (within about 0.02mm of 0.24mm across the part) and the pipe has come out better than expected.

However, the width has not done so well, being off centre (ignore the obvious gouge at the bottom left – I turned the handle the wrong way, you think I'd learn after a decade or so of playing with these things). It's possible that I was a bit too aggressive in the trimming, or that one side was climb and one normal.

The part has lifted off the fixture, but not until the trimming / drilling. the drilling certainly lifted the part as the drill broke through. I think I can fix that by having a clamp with a 3mm hole applied before the drilling.

I might have another try with smaller cuts for the trimming and a consistent direction of cut. Failing that cut to an outline and finish with piercing saw and files.

Iain

[Dave SParticipant @daves59043]

Last time I made a watch hand with a pipe I turned a disk with the pipe in it, then cut away the excess using a jewellers saw.

Bit of filing later and I had a small seconds hand for a pocket watch.

Will see if I can find the pictures.

Dave

[JasonBModerator @jasonb]

I thought I would have a go at the "start with something solid and saw it off" method. Not having any flat carbon steel stock I opted to use some silver steel and drew out a rough watch hand to similar sizes mentioned in the thread. Boss is 2.5mm dia x 0.75mm high and the hand is 0.25mm thick and sized to come out of a piece of 5/8" SS.

Having something solid to start with means you can take decent size cuts with a reasonable size cutter that is unlikely to break. Although I used the CNC similar could be done on a manual mill or even as mentioned above turn and bore the boss on the lathe and then mill the profile of the hand. Cutting parameters in the description below the video on Youtube

I mucked up the height on the first attempt at sawing off the hand and ended up with a poorly shaped one of 0.03mm thick

Luckily there was enough of the profile to have another go and this one came out 0.25mm as it should.

[Iain DownsParticipant @iaindowns78295]

That's brilliant, Jason.

Mind you one of my earlier attempts was simply to slice off a 0.25mm sliver from a piece of silver steel. It failed miserably – the saw ran up into the top surface almost immediately. So I abandoned that idea, clearly too early.

I shall have another go. However, today is going to be about replacing the water stop tap as it comes into the house (in a most awkward position) as it has sprung a tiny little leak. Last time I had a problem it was due the installer not tightening the connections up properly and it spent some weeks or months dripping into one of my servers until the motherboard rusted! Obsolete board, (obsolete) hardware RAID 5. It took me a week just to reconstitute the hard drives (not to mention the cost). Not that much damage this time, but I can see interesting times ahead

Iain

[Iain DownsParticipant @iaindowns78295]

I've tried your method, Jason, and have made some progress.

Essentially, set up is as above, but with a 20mm silver steel bar in a (new chinese) toolmakers vice on the rotary table. And all manual…

Broadly, this worked well, but when I came to cut off the hand, the hand curled up like a little snail. In earlier messing around on the whole bar I found I could reduce this buy keeping it cool and taking it slow. Not so with this little hand.

It's not really uncurlable to dead flat (at least I don't know how). Uncurling results in a rather lumpy affair. My next attempt will probably include placing some kind of fixture on top of it to keep it in place, though I'm not entirely clear, yet, on how that will work.

For those who were interested in my waterworks (the stop tap variety), in the end this proved rather simple and actually took less time and made less mess than I expected, which as my wife will tell you is very unusual!

Getting closer!

Iain

[Martin ConnellyParticipant @martinconnelly55370]

I think the point of running the saw down each side as mentioned in Jason's post of 10/7 (the one with a video) is to reduce this curl. I also think you need a very evenly sharpened slitting saw blade with no uneven wear on any of the cutting tips. Such wear will create forces that push the blade off line with the potential result of the part curling. Did you use a new blade or one that has already been used for another job? I also suspect that a thinner blade will induce more curl than a thick one, but this is only a guess based on a thicker blade being more rigid.

Martin C

[Iain DownsParticipant @iaindowns78295]

My slitting saws have seen very little use. the one I ended up using here has at most been used 2 or 3 times before. My original practice attempts (on an uncut 20mm bar) were disastrous. this due to my two 0.5mm blades being distinctly wavy. The latest attempt used a 1mm think 80mm 100 tooth saw.

I've also seen quite a bit of both lateral and angular run out. my best attempts are seeing something like 0.02mm at 12mm (vertical deviation) from the centre of the arbour (where the saw sits) and thus 0.15mm or more at the blade end. Not sure if this is adding to the issue or if this is reasonable for hobby kit.

I note that both of Jason's attempts have some curl, though he's certainly doing better than me!

Any suggestions welcome, of course.

Iain

[Ady1Participant @ady1]

Would a support collar give you more luck, a tube with a lengthways slot

So a 4mm collet has a 4mm collar with a 1mm hole

The collar extends to the last 1.5mm of the cutter

Edited By Ady1 on 01/08/2023 10:10:32

[Iain DownsParticipant @iaindowns78295]

Sorry, Ady – I'm afraid I don't get what you're saying…

Iain

[Anonymous]

Posted by Iain Downs on 01/08/2023 09:45:08:

I've also seen quite a bit of both lateral and angular run out.

Decent quality slitting saws, on a good arbor, should run with negligible side to side wobble. Radial runout is another matter. Even on industrial machines, and arbors, they run out enough to hear the change in note as the saw rotates.

Andrew

[Ady1Participant @ady1]

Posted by Iain Downs on 01/08/2023 10:02:07:

Sorry, Ady – I'm afraid I don't get what you're saying…

Iain

The cutter gets support along 85% of its length, only the business end is unsupported

I've been looking at trying it out myself after the other 307 jobs are done but it's at the precision end of the spectrum to get it right and Ady the bodger lacks time

Tapering the hole slightly may also help, drill it through with 0.9 and drill the rear half with 1.0, again time and precision required, and a good drill set

Edited By Ady1 on 01/08/2023 10:21:18

[JasonBModerator @jasonb]

To keep blade wander as small as possible you could go down to a much smaller dia blade on a part like this depending on what clearance your arbor has something like 40mm would be a lot stiffer. Might even work with a small Woodruff or tee slot type cutter.

The first one showed a lot of curl, as I said I got the height wrong and top of blade was near enough level with top of work so was really just pushing up a burr.

[JasonBModerator @jasonb]

Better way to support a larger 80mm slitting saw would be two large "washers" say 60mm dia which provided they were true to a good arbor would reduce blade flex

[Iain DownsParticipant @iaindowns78295]

HI, Ady. I was confused because the discussion was about slitting saws. The milling aspect seems rigid enough.

Thanks for the suggestions Jason and Andrew. I'd need to cut out of a rectangular bar rather than a rod with a smaller diameter, but I think I have a piece of silver steel I can use.

I'm going to recheck my spindle and collet run out first though. If they are out then a smaller saw may not be enough.

Iain

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