Abusing my micro-mill : and getting away with it?

The project I've slowly been working towards is to build a wood lathe.

I've got some 40mm bar for the spindle and 4 bits of 150mmx150mmx20mm to make the headstock from.

Basically, the idea is to square up the 4 bits, make a box and bore a hole for the bearings.

In hindsight, I've realised that my mill has a Y travel of 4 inches and the steel is 6 inches wide.

I've tried to surface it with a flycutter, but that stopped when it broke my mill (plastic gears). When I looked at the flycutter it appeared that I'd managed to wear the cutter flat fairly quickly - without much impact on the steel, and it may have been the pressure trying to get the damned thing to cut rather than the actual cutting of the steel that laid it low. Still, I'm rather nervous of trying this again (though I do have a handy stock of gears, now).

My second thought was to mill a channel on each of the four edges about an inch wide and 2 mm or so deep - do that on both sides. Then mill the centre part flat and parallel on both sides (taking off 1mm). Finally recut the channels with the centre area providing the registration.

In theory this should work with all the surfaces ending up parallel, but it's a lot of mucking about and clearly getting round a problem to which the solution is a bigger mill or a rethink. Or perhaps building a small traction engine instead...

I may have another go at the flycutting, but I had thought the contour of the tool was reasonable given the various (conflicting!) recommendations on the interweb.

The plates are from metal bits and mild steel, though I don't have a specific specification.

They are black and I wonder if taking off the surface with a sanding belt would help my case.

Sorry, this is a bit long, but I didn't really want to start a tedious process if there was a way round it!

Iain

Get a 5lts can of patio/brick cleaning acid and leave your plates in there until the black mill scale drops off, 30-60mins then it will be easier to machine.

J

You give no indication of how you intend to connect your four slabs. If this will involve welding, you need to take advice from your welder about how the edges to be joined should be shaped. You might find it helpful to do this before you spend further hours (and gears) removing metal which may not need to be cut away. And remember that once welded your slabs will not be exactly flat or parallel, so machining after welding will be better.

I am guessing about the welding but no clue is offered. If you intend to bolt the parts, it would only be needed for the areas in contact to be flat, saving time etc.

Cheers, Tim

Thanks Jason - I will try the cleaner.

Tim. You make a good point. I'm not planning to weld them. I lack the skills or contacts. It's bolting all the way.

I wanted at least two faces to be flat so that I could bolt them together and bore through. But you're right - I only need 2 faces and some of the edges (actually, I'm much less worried about the edges, but I'd do them all to allow joining to other things, neatness and so on).

That reduces the effort from 8 faces to two, which pleases me considerably!

Thanks

Iain

How fast are your running your fly cutter?

At >6" diameter, say 20" circumference, and HSS cutting speed of 90 feet per minute you are looking at about 1 rpm. With a feed rate of 0.004" that's going to take you 25 minutes to clean up one inch of six-inch wide plate.

In other words, although you can probably get away with slightly faster rotation and feedrate for light finishing cuts you are still probably blunting the tool by working it far too fast, because you will go crazy trying to work it at a sensible speed.

You are better off using a multi-tooth milling cutter which you can feed much faster and take multiple passes.

Neil

Neil

I think your maths has gone astray. A 6 inch hss fly cutter should, I think, be run at 60 rpm max, not 1 rpm.

Mike

Yep about 60rpm would be more like it, you would not turn 6" dia steel at 1rpm would you?

Infact a smaller flycutter swinging say a 2" dia would be quicker add less sensative to tram, 3 quick passes will cover the surface. Thats what I tend to use and prefer it to a multiple tipped tool for steel.

Edited By JasonB on 29/03/2016 20:06:46

What Uncle JS has to say about abrasive mill scale and pation cleaner here

Also very good for cleaning up after silver soldering and it shifts Tenacity No 5 no problem

I'm a silly s***, I was thinking one rotation per second!

Styill four minutes to feed an inch...

In order to face the entire piece I need at least a 2 inch diameter cut (mill has 4 inch Y travel, plate is 6 inches).

So I can get away with a 2" flycutter or a similar size end mill. That would be 180 rpm and a whole 3 inches in four minutes. As an aside, one of my tooling projects is to add a stepper to the mill which would make the whole process somewhat more palatable. I'm probably a bit concerned about the wear on an HSS tool over an hour's fly-cutting though. Not conducive to an even surface?

My attempts to use a 1.7" carbide tipped end mill were not particularly successful (counted in gears) albeit with metal of very dubious provenance. Having said that, the finish was rather nice - but it's still a tad too small even if it works.

With a flycutter what depth of cut should I be looking at? I think one of the problems the first time round was that I was scraping rather than cutting.

Iain

A tip you may find useful when fly cutting,if the facility exists on your machine, is to apply a small amount of friction to the spindle using the spindle brake whilst cutting. This ensures that the gears are always engaged and prevents them from bashing themselves to death. It usually eliminates the ripple finish sometimes experienced at the start of the cut. Roy M.

Why machine the entire face? If the edges are machined and a strip along the face where the edge will sit.....

Should all bolt up square.

Pete

Why use steel? For a wood lathe aluminium would be plenty rigid enough. Why use a fly cutter? It might be quicker, more accurate and easier on the mill to use an end mill.

Thanks for the tip, Roy. My mill (CMD10) barely has a motor, let alone a brake! I get your point, though and a little bit of cloth may server that purpose OK.

Peter - I can certainly machine two strips on the edges, but I'd have no guarantee that they were in the same plane. I'd have to move the plate 3 - 4 inches between each strip, with bits hanging of the edge of the table in both cases. Given that the rear would be unmachined (and is quite rough), the two cuts could be somewhat out of alignment.

To be honest, I've no idea how out they are likely to be, so perhaps this is less of an issue than I think.

Also, thinking about it, I could mill in the Y axis. This would let me mill in one operation, except for one inch either end which I could then mill out deeper in a secondary operation, leaving a recess at the corners. That should allow me to bolt squarely, though with some loss of rigidity, which I could perhaps recover by adding a lid.

Hmm.

Iain

Cloth and rotating spindles are not a good combination. The traditional method is to take a piece of wood, say 1" x2" x 2 foot long and put one end up against the column of the machine and then let the side of the wood rub on the end part of the spindle or collet chuck, in a non-critical area. Apply gentle hand pressure to the wood, it does not take much to take up the "clunk clunk" back lash and make life much easier for the gears.

In less time than it would take to drive to the shop to get patio cleaner, you can take a 10" coarse file (bastard) and using one edge of it, ie with file canted at an angle instead of laid flat on the job, you can scrape that black mill scale off. You can even grind the end of the file into a slight angle to make a crude scraper for any tough spots.

Hi Iain,

It took me a while to read through this thread, all the time thinking and picturing that you were trying all of this on a 'mini-mill' which usually translates into an X2 ...until I read that you have a CMD10, which is a 'micro-mill' = X1 variety.

No wonder you used the term 'Abusing' for the thread title and pointed to braking gears etc..The idea of a small Fiat pulling a king size caravan comes to mind..I wish you good luck on the journey.

If okay with you and the moderator, I would request that the title of the thread is changed to 'micro-mill' in place of 'mini-mill', as it definitely paints an inaccurate picture. No disrespect intended to the thread or the author.

Ketan at ARC.

Hi Iain,

Following comment is designed to be helpful:

Your machine has a 150W Brushed D.C. motor, with good torque, especially in the low gear setting. ARCs similar offering to a CMD10 is the SX1L, which has a longer table and bigger cast base. In the early days when ARC started selling these machine, an airline pilot friend of mine 'poo poo'ed' the mill, labelling it as the usual Chinese crap. He said: 'I bet you that this machine has no torque...it only has a 150W motor'. He was confusing AC with DC and he failed to take the low gearing into consideration. I put the machine in low gear and started running the machine at low speed. He decided to prove the point by trying to grab the spindle and stop it with his big hands. Initially, he failed. He had to put a lot more pressure, and reduce the speed to near zero, before he succeeded.

For H&S reasons, I cant possibly suggest that you try this Iain. The point I am making is that it has great torque, proportional to the size of the machine, but it is no mini-mill or Bridgeport.

After abuse occurs, broken gears etc., faults can/do creep through the electrics/motor, resulting in loss of torque in certain cases. Being a micro-mill, there is a limit to how much abuse the set-up can take, be it electrical or mechanical. Certain people try carrying out the above test after such gear breakage occur, to see how easy or difficult it is for them to stop the spindle in low gear by grabbing/putting force on it with their hands, at relatively low speed. If it stops easily, it would be a good indication of loss of torque due to damage/fault developing in the circuit board/motor.

Again, for H&S reasons, I cant possibly suggest that Iain or anyone else try this, and usual disclaimers apply to all of the above comments. Most of us are guilty of abusing our machines, but prevention is usually better than cure, which can be costly.

Ketan at ARC.

Hardly surprising when the spec for that machine quotes: "Mill capacities - Face 20mm, End 10mm"!

Russell.

Iain,

Forgive me for asking ... [the answer is presumably 'because I want to'] ... but why are you making a Wood Lathe, using micro-size machinery ?

A quick look on ebay, etc. should find you a Record or similar lathe with a cast iron headstock. The detailing on these lathes is not good, but it would be much easier to 'improve' one than to start from scratch.

MichaelG.

.

Edit: Here is an example ... but they are often cheaper.

Edited By Michael Gilligan on 30/03/2016 12:29:29

Thanks, all.

Well. I've taken up model engineering 'because I want to'. I enjoy learning how to do things and making tools.

It's slightly easier to explain all this to the missus if she things I'm making *something*.

I will readily acknowledge that I should have started somewhere else, but I've bought the tin now and got the bit between my teeth.

I'm also happy to tell you that I wish I'd bought a bigger mill. Much bigger. That will surprise the lot of you, I have no doubt!

Perhaps I will buy a bigger mill, but I would need to get budget approval from her indoors which means I need to show something that she regards as a project!

In the meantime, it's about the journey not the destination, but I suppose the journey won't be helped if the wheels fall off.

I'm kind of intrigued by the challenge though - and fascinated by the wealth of knowledge and suggestions (and how you all manage to stay polite which I'm clearly mad!).

I'm away for a bit but I will report back in a couple of weeks.

Iain