[dharmic]

Had some fun last weekend, was cutting some parts for a couple of 2x72" belt grinders a mate and I are making for ourselves.

Very tentative at first but turns out the Omio plays nicely in mild steel. I was surprised and impressed.

Carbide 3mm 2 flute cutter, 10,000RPM. Helixing in on a 2.8mm diameter, then cutting at full depth 6mm, 250mm/min on an adaptive toolpath that looked to be about a 0.25mm radial WOC.

Munch, munch, munch with a fairly good finish even before I did a spring pass at the end.

One cockup had it ramp into a full depth slot cut - surprisingly, the tool didn't just break before I managed to hit the feed hold and pull it out of there. Given the racket it started making I suspect it wouldn't have lasted long trying to do that though

[jo_ky]

That's useful, thanks! What was the feed rate and angle for the helix? Any coating on the carbide bit you use?

[dharmic]

Good question. 2º ramp, 100mm/min for the feed-in rate. No coating - I bought these bits for aluminium work which wants sharp edges, coatings dull the cutting edge. Could have sped things up with a coated cutter, I guess.

These cutters I'm getting from the Klot Tool store on eBay (seller danyazhan0) and I've been really pleased with how well they're going for the price. Only downside is the typical 3-4 week wait.

[Mmpie]

Good question. 2º ramp, 100mm/min for the feed-in rate. No coating - I bought these bits for aluminium work which wants sharp edges, coatings dull the cutting edge. Could have sped things up with a coated cutter, I guess.

These cutters I'm getting from the Klot Tool store on eBay (seller danyazhan0) and I've been really pleased with how well they're going for the price. Only downside is the typical 3-4 week wait.

Interesting. I think I need to buy another spindle, and try this. This could save me a massive headache, I wouldn't have even bothered trying on the OMIO without this heads up, so cheers.

Is it a leaded/free machining steel you used or just plain old normal mild steel?


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[dharmic]

Correction - they're TiN coated, damn, about $15 a go and stupidity has cost me a couple. Impatience will probably cost me the next one as I attempt a ramp in and full depth slot cut.

Mmmpie not sure of the steel, it's galvanised plate from the scrap dealer around the corner. It'll be the cheapest nastiest rolled gal plate they can get their hands on, I'm guessing something like a GS250. Guarantee it won't have anything in it to make cutting easier.

Oh yeah, coolant is a pulse misted 20% ethanol in water mix with a teaspoon per litre of soluble oil thrown in for a touch of lubricity.

[Mmpie]

Correction - they're TiN coated, damn, about $15 a go and stupidity has cost me a couple. Impatience will probably cost me the next one as I attempt a ramp in and full depth slot cut.

Mmmpie not sure of the steel, it's galvanised plate from the scrap dealer around the corner. It'll be the cheapest nastiest rolled gal plate they can get their hands on, I'm guessing something like a GS250. Guarantee it won't have anything in it to make cutting easier.

Oh yeah, coolant is a pulse misted 20% ethanol in water mix with a teaspoon per litre of soluble oil thrown in for a touch of lubricity.

Nice, so in theory a nice chunk of leaded flat bar should machine quite easily... with a decent spindle. This one I have currently is a pile of crap, 3mm carbide hits its limit at a similar engagement in 6082 al. 3mm axial 0.5mm radial is as hard as I can push it before they start breaking at a feed rate that is teetering on a very fine line between cutting and rubbing, the run out is horrifically bad.


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[dharmic]

I'm finding out now, by comparison, just how nasty aluminium is to cut. Zero forgiveness on stupid moves with the mild steel but none of those "drop in spindle note giving you 1.28 seconds' warning before the gummy cutting edge bites hard and snaps the tool off" shenanigans that you get with ali.

[RCaffin]

Gummy aluminium - yeah, but that means you are using the WRONG alloy. 5000-series or below are a pig to machine. CP is a disaster. 6000-series is fair to good, and cast aluminium tooling plate is a delight. Fortal is wonderful.
A polished aluminium-specific cutter is preferred. Do not use it on steel.
(Pulsed) misting with some oil is very desirable: I use kero/olive oil, 3:1. Skin compatible (well, the oil is).

Cheers
Roger

[dharmic]

I wasn't clear, sorry. I use 6061 and it's fine with sharp uncoated cutters but it still gums up occasionally when a toolpath blocks the mist path or allows buildup of chips in the way. My comment was more the contrast of the steel compared to the aluminium makes the ali look gluey.

[RCaffin]

With aluminium I usually have the mist nozzle pointed down at the tip of the cutter. The mist is pulsed, but the air blast is continuous.
I find 6061 usually OK to machine, with pulsed misting. But I understand what you mean re steel.

Cheers
Roger

[Mmpie]

With aluminium I usually have the mist nozzle pointed down at the tip of the cutter. The mist is pulsed, but the air blast is continuous.
I find 6061 usually OK to machine, with pulsed misting. But I understand what you mean re steel.

Cheers
Roger

How do you get your pulsing to work well? I've had my reservoir and lines set up a couple of different ways but every time I close the solenoid, the lube line continues to empty, and then takes a good few seconds to refill upon reopening the valve.

I generally just leave mine on, the constant liquid flow works well to wash any chips off the walls of the part, the downside is it leaves a sticky mess to clean up.


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[jo_ky]

For my Kool Mist, I was planning to zip tie the coolant and supply lines to the outside of the cable carrier on the gantry (since it's full), and then run them loose from there to the compressor supply line and to the coolant tank, perhaps with a spring mechanism to take up slack. But 4 feet isn't enough, even for that half-way solution.

How have others solved this problem?

The fittings on the hoses are 1/8" FIP. Will I need to reseal the threads on the valve block if I replace the hoses? Right now, I can't even get the threads to budge.

[Mmpie]

For my Kool Mist, I was planning to zip tie the coolant and supply lines to the outside of the cable carrier on the gantry (since it's full), and then run them loose from there to the compressor supply line and to the coolant tank, perhaps with a spring mechanism to take up slack. But 4 feet isn't enough, even for that half-way solution.

How have others solved this problem?

The fittings on the hoses are 1/8" FIP. Will I need to reseal the threads on the valve block if I replace the hoses? Right now, I can't even get the threads to budge.

I run my air through the cable track. For coolant I just use a big jam jar on a shelf behind the machine with the line going through a pulley and a weight on the jar side to keep the line taut so it retracts as the gantry moves back. Works a treat and my coolant line is now only about 2'.


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[RCaffin]

Long explanation follows. I don't have a current photo - sorry.

Compressor to pressure regulator to small solenoid valve to LineLok hose to nozzle.
I find the PReg valuable as it lets me control the level of misting.
M8, nominally Flood coolant, has been repurposed to be Air Blast. Makes no diff to Mach3.

Misting:
A glass bottle with a sealing lid sits on top of the mill - above the nozzle. This holds the kero/olive oil mix.
There are two pneumatic fittings in the lid. One takes has a dip tube on the inside, to the bottom, and on the outside there is a 1/8" delivery hose going to the misting valve. The second fitting has a long length of flexible silicone hose attached.
If I have just refilled the coolant reservoir, the delivery tube will be empty. I open the misting valve and blow into the 2nd hose. Since the reservoir is sealed, this forces coolant up the dip tube and down to the misting valve. Easy priming. Since the hose is 'sealed', it stays filled over time. Since the bottle is just a little above the nozzle, there is a slight delivery pressure

From the misting valve there is a fine PE hose going down to the LineLok nozzle. This is tied to the outside of the LineLok. Just before the nozzle there is a small hole drilled at an angle in a LineLok segment, and the PE tube has been pushed through this far enough that it emerges from the tip of the nozzle. By making the hole a tight fit there is little or no air leakage and the PE tube does not move.

I adjust the PE coolant tube so it sticks out of the air nozzle by about 1 mm. When air whistles out of the air nozzle it creates a venturi suction on the coolant hose. If coolant can flow, it is turned into a spray of droplets which hits the cutter and the job. You want a spray of droplets, not a fog.

The magic in this is that the coolant valve is about 400 mm away, and one might expect the hose length to be too long. But that is wrong. The PE coolant hose is sufficiently stiff that it does not compress under the very small suction pressure. If it was silicone it might - dunno. So a 1 second opening at the valve is translated to a 1 sec blast of coolant spray or mist at the nozzle.

There are some traps for the unwary. I cannot find really miniature liquid valves rated for kero, but I can find very small pneumatic valves. They are not 'cheap', but the AirTac brand from China seems to work well. It does look like a Festo valve. You can find even smaller pnuematic valves on eBay, but the kero caused the rubber seals in them to swell up and block. That's no good. You may have to experiment.

EDIT: I now have a free sample of what the vendor tells me should work with kero at these flow rates. I have yet to try it out. But they are US$150 - 200 each. Um.

Now, the controls. M8 turns the air on and off: that is simple. M7 turns the misting on and off, but I don't want the misting continuous - that uses far too much coolant. So ... M7 enables a 555 timer (I hang my head in shame, but they do work), which oscillates continuously at about 4 - 20 Hz, as set by a front panel pot. It triggers a second 555 which works as a single shot with a period of 0.4 sec to 5 sec (2nd pot). The output of this second 555 drives the mist valve.

Misting won't work without air blast, but the air blast is wonderful at clearing away chips from the cutting edge and preventing second-cuts. I issue M8, then M7. Two LEDs on the front panel tell me how it is all going. The Air LED just goes on and stays on. The Mist LED goes on only when the Mist valve is driven. If I need more coolant I can increase the pulsing frequency OR the pulse length. Cheating: I also have a manual overide button which turns the misting on as long as the button is depressed. I'm obsessive.

It all works in a semi-production environment.

Cheers
Roger

[Sterob]

Ok Roger....Get ya camera out.....
Sounds like a good setup.


Steve

[Mmpie]

That's a well thought out set up Roger. I remember you posted pics some few hundred pages back in the thread. I wonder why you don't use normal soluble cutting fluids? At least here in the U.K. You can pick them up in small 1L or 5L bottles for not much, and diluted 10:1 you barely use any with mist so the expense is nominal at worst, particularly when pulsed like yours, mine is just always on and I've used about 2L in a year or so.

Here's a pic of my setup, it's a bit crude and made out of cheap bits and bobs I could get my hands on locally the day I set it up, but it works and doesn't leak so it will stay how it is. I actually have a bigger mill on order so I might do away with it altogether and just use the OMIO solely for wood and plastic sheet work.




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[RCaffin]

I wonder why you don't use normal soluble cutting fluids?
I remember asking a very good friend of mine years ago - a super techie working for me who taught me what I know about machining, why his fingers were covered in band-Aids. The cutting fluids in the shop were sufficiently harmful that they were cracking his skin and causing quite severe discomfort at times. Kero does not do that and olive oil is skin-friendly, and with pulsed misting parts come out almost dry anyhow.
So it is not the cost, it is my health.

A big difference is that I use far smaller tubing and fittings, so everything is a lot more compact. Yes, of course one loses some pressure with thin hoses, but the compressor makes more pressure than I want anyhow, and I do not use a large air flow, just a focused one.

Photo - sigh. The machine is currently set up for machining timber prototypes and basalt real things. I don't bother with coolant for the timber, and the basalt machining is done under a good water flow. So the pulsed misting has been nudged to one side for a bit.

Both materials need the spindle on a high speed for some time (many hours), so I have had to add a coolant jacket around the spindle to stop the bearings from going above 'warm'. Dual AC bearings 7208, 40x18x80 mm, largish. That uses recirculating water.

Cheers
Roger

[jo_ky]

If I get a 4th axis assembly, what reduction ratio do you all think is most useful? The one I'm looking at would be an 80mm 4-jaw chuck, and I can choose between 50:1 and 100:1 for the gear ratio (it's a harmonic drive). If I choose 50:1, then I can match the X/Y top speed of 4000 mm/min for diameters down to 10mm, and get a resolution of about .03 mm / step for the largest diameters. That seems good to me! Anyone think the higher ratio is worth it? The stepper is a 3A Nema 23.

[mach-mate]

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[RCaffin]

You could start with this:
Build Thread The Design and Construction of a 'Backlash-Free' Rotary Table
Disclosure: I wrote it.

I found 50:1 reduction was in the HD was fine, but I had a bit of reduction between the motor and the HD as well. Part of that was to get a clean value for the angle/step. No special reason; I just wanted to.

Cheers
Roger