Setting up a Mini Mill & Stuart 10V Machining

A few notes:

I normally aim for a thou or less when tramming my mill, over a diameter of 200mm or so.

No idea what happens if I lean on the table after adjusting the gibs; never felt the need to measure it. My manual mill is pretty worn so adjusting the gibs is a compromise anyway. I just do it by judging a slight 'drag' when moving the table.

The manual mill is a knee mill and the column is large by hobby standards. The CNC mill has a conventional column but I've never leant on it to test. I just make parts.

The machining marks are indicative of a blunt or pooly ground cutter. Where did the cutter come from? Is the cutter HSS or carbide? Your speeds are a bit fast for HSS but slow for carbide. If there was vibration and noise something is wrong. As before a worn of poor quality cutter, or the most common early error is feeding to slowly. Rule 1: the cutter needs to cut not rub. Rule 2: cutters are consumsable items, don't try and make it last for ever by pussyfooting about on feedrates.

I wouldn't bother with cutting oil, especially if it isn't flood coolant. If it is applied in dribs and drabs it just makes a s sticky mess which is sure to cause re-cutting of the swarf, damaging the cutter and making a mess of the finish.

Machining a block to an accurate thickness on a mill is seemingly simple, but is much more difficult than it looks. Even if the mill is perfect the results are highly reliant on how the work is clamped and the quality of the machine vice, if used. If I get better than 2 thou on a 6" square I'm happy, and that's on a large mill with a industrial quality machine vice.

Andrew

PS: If I've an edge finder and DRO available I wouldn't bother marking out and centre popping. Just zero the DRO on a convenient corner, move to hole position and drill - quick 'n' easy.

Edited By Andrew Johnston on 07/05/2020 16:37:55

Which gib were you adjusting? At one stage I bought an SX1 for CNC conversion, same table as the SX2P I think, and the gibs were appalling. At least for the Y slide, I machined a new gib from 1/8 brass strip and it was much better, I disposed of the X1 when I bought a Novamill. I think the X slide gib might have been a bit better, but the Y one was made of metal that was too thin and bent.

Jason is the expert here, but I agree that the cutter is worn to get that effect. When I started I was very careful about using slow speeds and feeds, but cutters work much better when you apply some welly.

I agree with Jason on this - just make some parts.  Someone I know made a 10V where he "machined" the bedplate on a sheet of emery on a piece of glass.

Edited By John Haine on 07/05/2020 16:48:21

Thanks very much Andrew.

I fully appreciate that making parts is more relevant than messing about chasing an impossible setup. However, my lack of experience means that I want to at least start with a setup that's in the right ballpark. I'm trying to determine where I am with that by initially making small parts for the mill, like the gas-strut mount, and the vice clamps, and doing some simple test pieces. Believe me I want to start on some real work asap.

The cutter was an HSS slot drill.

When you say machining marks caused by a defective tool - do you mean the swirls, or the ridges, or both?

It wasn't rubbing - definitely cutting. Any advice on rpm for this diameter and depth of cut?

I did indeed end up with a sticky mess of oily swarf which I'm still cleaning up...

I marked out the centre of the work because I have to admit I've never really done it before, and wanted to check that

a) my marking out method was accurate,

and

b) that I could use the edge finder and DROs properly.

I hope that I haven't made two random errors that happened to coincide in one point!

John,

It applied mostly to the x & y gibs. The z-axis is so heavy and has an overhanging load so I just did the best I could by feel rather than with a DTI.

TBH I'm more concerned with the potential tramming issue, but first I'll make another of the four clamps with a different cutter and see what that's like.

BTW who is Jason?

Thanks.

A rule of thumb for HSS cutters in low carbon steel is 100ft/min cutting speed. For a 10mm cutter that's about 970rpm. Slightly slower is better than slightly too fast. A depth of cut of 0.5mm is small, but should be no problem. How do you know it was cutting? I'd be feeding at 100mm/min or more. If you know the pitch of the leadscrew you can work out how many times a minute you need to turn the handle.

The swirls can be produced by several issues. First as the tips wear, or if they're badly ground in the first place, they will cut inconsistently. Second, dragging swarf around with the cutter scores the work as the swarf gets trapped under the cutting edge. Third, the material matters. A 'sticky' steel like EN3 or hot rolled steel is much more prone to this problem than EN1A. The ridges between cuts imply that the cutter isn't cutting cleanly. Assuming the mill is trammed, you shouldn't be able to feel any ridge. Do you know what spec the steel is?

Fair enough on the marking out. Ahem years ago I was taught marking out and centre popping but now I only use it for sheet metalwork, where I'm cutting/drilling by hand. But of course one needs confidence before flying with no safely harness.

Andrew

I wish I had had a dti when I made my 10V, steel rule, firm leg calliper, 100mm square I made myself and an ancient rusty micrometer were all I had

Expect I have similar movement in my table if I were to push and pull it but I like to run with a fairly loose X axis anyway

Tram is within reasonable expectations, I have a bit more lean the the X3 than the SX2.7 but it's has not stopped me.

2-flute cutter not ideal for facing, try less overlap, about 2/3rds cutter width and a finish pass of half that depth. As soon as a cutter looses its edge or does not come with a sharp edge if really cheap then it starts to ride up on the surface and can give both the swirls and steps

Without knowing what the bottom of the block was on hard to comment on thickness, tool being pushed off the surface it won't be cutting where it should.

Machine as setup should be capable, the rest is down to you.

Edited By JasonB on 07/05/2020 17:15:07

Amazing, being quoted and he hasn't even posted in this thread. That's definitely action at a distance.

Search for member JasonB.

Andrew

Bother, shouldn't have taken the time to proof read.

Edited By Andrew Johnston on 07/05/2020 17:17:25

Edited By JasonB on 07/05/2020 17:39:43

If it's blunt then the finishing pass won't be worth doing, even more likely to just ride over the surface.

Here is a good example, slot on the left cut with a blunt cutter, one on the right with the same cutter after shapening.

I would suggest getting a fly cutter as part of your tool collection. A number of people (including me) use insert tooling in them with good results. This has been covered in other threads in the past.

With a fly cutter smaller items can be faced in one pass and often the trailing edge does not reach the workpiece so less chance of the sort of finish you have got.

Martin C

Fly cutting thread

Link added

Edited By Martin Connelly on 07/05/2020 17:56:40

It was generating chips, so I assume it was cutting OK.

I can't remember the grade of steel. I bought some blocks about 15 years ago to practice on, I asked for stuff that was easy to machine. It so happens I can get 2 clamps out of each block once theyre sawn in half.

I'll try a lower speed.

Thanks.

Martin,

Thanks for that - noted.

If I'm cutting cast iron, intermittently, is a carbide tip going to be OK?

Just looked at fly cutters on Arc Euro. If I got an R8 version, do I need a special 8mm insert tool, or can I use a standard lathe tool?

Thanks.

Left hand lathe tool if you want to run insert tooling or the HSS-Co5 tool ARC do cuts well enough, I usually just go with HSS

I've never broken an insert with intermittent cuts on the lathe or using a fly cutter on the mill but do take it easy on depth of cut until it is continuous cutting. As Jason says use hss and you may find it is fine and its cheaper than inserts if the cutting edge needs to be sharper. The use of insert cutter or hss may depend on lots of factors and what is best may depend on material and machine as much as anything else. Cast iron cuts nicely but can be supplied with a hard surface scale that can take the edge off hss very quickly. This has been covered in other threads that are worth looking for. You need to get under it to remove it.

Martin C

Inserts should be fine if you want to go that way. plenty of face mills using them and the insert does not know if it is on its own or several in a head.

Thanks guys. A long time ago I did some fairly simple 'work' work on the ML7, and was given a set of Sandvik tool holders and inserts. I've got a left hand holder, so I might go for an R8 holder and see how I get on. BTW genuine Sandvik inserts seem to be eye-wateringly expensive, so I ordered some cheaper ones that should fit.

Re. continuous cuts - I doubt there will be any on the 10V. I want to start on the base and bearing plate, which as you know are just hollow outlines really.

Is it worth removing the casting skin on a linisher first?

Not of you are going at it with carbide and going buy the recent comments you may not have much to come off anyway.