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Small Milling problem

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Wolfie30/01/2012 18:49:05
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Elsewhere I bemoaned the fact that I was struggling to mill a small slot accurately.
 
I've been having another go at it today and lo and behold got it wrong again. TWICE

Anyway I think its down to the fact that the smallest slot mill I have isn't small enough so whichever line I line it up on, or whichever side I measure from its wrong cos my mill is wider than expected.

Now the required slot width is 3/32" but the smallest slot and end mills I have are 3mm. I just had a look at a tool site and the smallest they sell are 3mm or 1/8. Not small enough. So any suggestions as to how I go on cutting this slot??

The stock from which I am starting is 3/16 square bar and getting rapidly shorter Its quite difficult to hold too as the finished item is only 3/8" long.

Edited By Wolfie on 30/01/2012 18:49:59

wotsit30/01/2012 19:01:47
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Wolfie,
 
3/32 inch is ~2.38mm, so your slot mill is too big. Is it possible for you to (carefully) chain drill along the required slot (say 1/8 inch), then use a fine needle file to clean it out? The slot cannot be too long, if the finished job is only 3/8 inch long.
 
Machine tools are all very well, but sometimes hand work can be just as quick and good.
 
I think I saw someone elsewhere on one of your queries suggest starting with a wider piece of metal. I would say that is definitely a good idea when you are making such a small part. Mark it out (the slot) on a larger piece of metal the correct thickness, file to shape, then mark out the required 'outside size' and cut it away. The larger piece of metal will be much easier to hold than a tiny piece 3/16 inch square and 3/8 inch long. (I don't even think I could see that properly these days ).
 
 
jason udall30/01/2012 19:02:03
2032 forum posts
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Wolfie...Ever heard the joke..if I were going there I wouldn't start from here....?
What you are looking for at 3/32" sounds more like a slitting saw...bought in at the notional thickness.
Diameter and hole size to suit job and or mandrel. Or make mandrel to suit ...but if in effect putting a screwdriver slot in the end of some thing slitting saws the thing
Though 1mm slot drills are made but spindle speeds are horrendous
wotsit30/01/2012 19:09:11
188 forum posts
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Hi again , Wolfie,
I just saw Jasons post, and I think we need a bit more explanation - I assumed it was a 'closed' slot you were making, hence my description. I think Jason is describing cutting an open-ended slot (like a sawcut in the metal), which as he says is much easier with a slitting saw.
 
So can you elucidate a little?
JasonB30/01/2012 19:12:18
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Wolfie I use the 3 flute disposable cutters, they go a lot smaller than 3/32" have a look at this or you could go down to a 2mm one and then take a whisker off each side of the slot.
 
J

Edited By JasonB on 30/01/2012 19:13:02

mgnbuk30/01/2012 19:15:15
1394 forum posts
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I just had a look at a tool site and the smallest they sell are 3mm

Try another tool site - endmills & slot drills are readily available down to 1mm.
 
We use these (the coated variety, mostly) at work :
 
http://www.cutweltools.co.uk/files/ww/3%20flute%20slot%20drills.pdf
 
Very good service - most ex-stock & delivered next day. Imperial sizes are available too.
 
The 1mm ones do have a tendency to break just for the fun of it, though !
 
Regards,
 
Nigel B.
dcosta30/01/2012 19:29:15
496 forum posts
207 photos
Hello Wolfie.
 
You can find here a place in UK where You can find a 2mm 2 flutes slot drill HSSE 8% Co from a brand I like (IZAR) made in Spain. Their quality is the best I ever used (I'm not a professional).
I think You can download the complete IZAR catalog from www.Izartool.com
 
Regards
Dias Costa
Paul Barrett30/01/2012 19:55:02
59 forum posts
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FC3 cutters are what you want.
Ady130/01/2012 20:49:02
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You'll just have to buy a shaper and a filing machine Wolfie.
Terryd30/01/2012 21:47:56
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hi Wolfie,
 
Do You have a sketch of the part to show us?  A simpler solution may be to fabricate the part. two pieces of 3/32 thick material sandwiched between larger stuff and silver soldered. Make it oversize and mill or file down to required final size. - No expensive (or broken) cutter or potentially problematic machining processes (for a beginner) in sight.
 
There is always more than one way to skin that cat.

Regards

Terry

Edited By Terryd on 30/01/2012 21:50:50

JohnF30/01/2012 21:58:53
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Wolfie, Someone suggested FC3 cutters -- I use these quite a lot and you can mill small slots easily with these.
I have cut slots down to 1.5 mm and my spindle speed is 2800 max. Assuming a closed slot what you do is drill a hole first then the depth of cut is 0.001 or 0.002 inch per pass--yes it takes a little time but you can cut to the depth of the cutter and I have done this in steel.
If it was / is a long slot I would go for a slitting saw.
 
Good luck. John.
David Littlewood30/01/2012 23:06:52
533 forum posts
1 mm! Not really trying, these people sell them down to 6 thou. Not the cheapest, but they do sizes hard to get elsewhere and do super fast delivery.
 
Seriously, there shouldn't be too much problem using a slot drill of say 2 or 2.4 mm, you just have to treat it gently. High spindle speed - I would use 2000 rpm as it's the fastest on my machine. Maximum depth per cut say 1 mm on brass, probably better 0.5 mm if it is hard material*, and use neat cutting oil for steel. Use power feed if you have it, this will reduce the risk of uneven feeding overloading the teeth.
 
Yes, you could bodge it some other way, but you won't learn much about using your new milling machine. A decent milling vice (with a parallel to bring it up to height) should have no problem at all holding a piece of 3/16" metal, even if it is only 3/8" long.
 
Is your slot open-ended or closed?
 
David
 
*I personally think cuts of 0.001" are more likely to wear out your cutter prematurely; it is certain to wear out your patience!

Edited By David Littlewood on 30/01/2012 23:08:24

Ady131/01/2012 02:11:14
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When things get this small I would think that "zero backlash" techniques and strategies would become increasingly important
John Olsen31/01/2012 05:42:36
1294 forum posts
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I would remove as much material as possible by drilling along the line first. In any case it is really good to have a hole at each end of the slot even in larger work. (I'm assuming a closed slot here.)
 
As Ady says, controlling backlash and also keeping the feed rate really slow is very important. I am lucky enough to have one of those overpriced fine feed attachments, which gives better control at really low feed rates than I can do by hand. But before I had that I did the odd job like this by hand. I have some 1/16 slot drills...always buy more than one! I would put on more than a thou of downfeed, the usual guideline of about a quarter of the diameter should still be OK, but you want to be turning these tiny cutters as fast as you can. If you work out what the rotational speed should be, it is probably higher than the machine can do. This means keeping the feed rate down to avoid biting off too much. When you are doing the feed by hand, this means taking a lot of care and not being impatient.
 
There are attachments made to give a higher spindle speed for this sort of work, but they tend to be a bit too expensive.
 
regards
John
JasonB31/01/2012 07:33:03
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Its teh forked end to go onto a valve rod if that helps people visualise what Wolfie is trying to make, off a Stuart S50 I think.
 
Just one thought Wolfie how much metal are you taking off per pass, I know on your mill clamps you took a full 8mm depth of cut with a 8mm dia cutter. If you are doing similar with your smallest cutter it will flex sideways.
 
J
Wolfie31/01/2012 08:56:53
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502 forum posts
Ha! No not taking 8mm cuts any more, learned that one quickly.
 
Aye its the forked end piece for the S50 like Jason says (thus open ended) and I've made the bloody thing 4 times now grrr
 
The slitting saw sounds like a good idea, why did I not think of that.
Terryd31/01/2012 09:13:53
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1946 forum posts
179 photos
Hi Jason,
 
If it's an open ended slot as In a clevis, surely a slitting saw is the way to go?
 
Hi Wolfie,
 
is this the type of thing you are making?
 
Clevis

 
 
I made this one below this morning for fun and to test skills I haven't used in a long time. I had to mill down a piece of rusted 8mm bar to 3/16 (5mm actually). I then filed a groove across0 the middle of the end, to locate a hacksaw blade using the corner of a square file. I cut the slot down with a hacksaw with two blades in the frame which gave me a slot just short of 3/32" wide and then filed it to width with a flat needle file.
 
The whole thing (not including milling) took about 10 to 12 minutes, but then again I didn't bother with marking out, I just did it by eye and guessed the depth, so that would add some time. I just need to turn down the shoulder now. It is steel, the straw colour is not heat treatment but the cast thrown by the lighting in the kitchen.
 
My Clevis
 


 
Best Regards
 
Terry

Edited By Terryd on 31/01/2012 09:17:39

Tel31/01/2012 09:26:38
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157 forum posts
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Yes, a slitting saw is what you want for those - I have a photo series on making them on this page - be well worth you having a look.
 

Tel31/01/2012 09:32:37
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JasonB31/01/2012 10:10:06
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Yes as I said in the first post about positioning the cut a slitting saw is best but you will need to have a decent amount of metal to hold in the vice.
 
"Another way to avoid an overwidth slot is rather than mill it do it sideways with a slitting saw, again touch the saw down onto the work and calculate how far down to lower the blade."
 
But they could be done with teh clevis stood vertically and light say 0.020" cuts taken, as the slot is only 3/16" deep your cutter will reach. Will save you having to buy a saw arbor and blade for now
 
J

Edited By JasonB on 31/01/2012 10:11:27

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