New Mill - Starter Tooling

It would seem that T slot cutters are a real mixed bag, the one I have is HSS and maybe I was just unlucky. Having had a bit of a search I see HSS cutters similar size to mine at £50-£60 each mine was £13 so either some suppliers are racking up the prices or there is a real difference in quality..?

I have a job coming up in the future where I will need a dovetail cutter, the job is in steel and at the moment I am thinking carbide providing it wont break the bank. I would have thought HSS would be fine but how much do you need to pay for a good one, seems a bit of a gamble.

Ron

Edited By Ron Laden on 02/01/2019 08:26:28

The poor performance of the cutter could have been of my own making of course. The material was 6082 and the cutter 8mm deep and 16mm diameter. I ran it at 500 rpm, was that too fast..? Problem was, I couldnt run it any slower as the mill hesitated at 400 rpm and even at 500 I almost stalled the mill at one point. I did try it a bit faster but that just didnt feel right and made no difference. I used WD40 and kept clearing the build up of swarf but as the job progressed the cutter certainly felt as if it had lost its edge.

Ron, how deep did you go with the initial 8mm slot, you can reduce the load on the cutter if you mill that first all the way to the bottom of the slot or even a little beyond. Book speed for ali would be about 1500rpm but that would be on a big rigid machine.

They do need a bit of welly behind them, think what it would be like using a 16mm dia cutter to make an 8mm deep pass, that's quite a lot for a small machine.

Thanks Jason, thats probably where I went wrong, I only went 6mm deep with the 8mm slot. Stupid me, from what you say I can now see that had I gone full depth the T cutter would have only had to take out the sides, I was asking it to cut out a 8mm x 16mm slot in one pass.

Ron

Another trick is to cut the initial slot, maybe a little deeper than the final dovetail depth; then use a hacksaw guided by the bottom of the slot to cut to the full depth of the dovetail so that the sharp corners of the tool don't have to work so hard (or at all). That reduces the power required and also minimises the wear on the teeth tips.

Oh dear, there's still a lot to learn! Still, the cutter shouldn't have gone blunt working in 6082. Look at an industrial mill and, as John says, the central slot will be slightly deeper than the T-slot. One, it relieves the centre of the T-slot cutter and two, it provides clearance if a clamping stud sticks out slightly from the bottom of a T-nut.

Andrew

Certainly that's been my experience! When I started home metalwork seemed all my tools were made of Cheesium. Drills, hacksaw blades and HSS lathe tools had short lives. Then something strange happened - the tools all miraculously improved. Gradually at first but now they last much longer.

I put the improvement mostly down to gaining experience and taking advice. Cack-handed learners can and do ruin good tools. Some things that changed:

1. Prefer known materials to unidentified scrap
2. Understood better the properties of the materials. Steel, Brass, Aluminium, Cast-iron are not the same and they come in a bewildering variety of alloys with very different properties.
3. 'Let the tool do the work'. This is actually complicated and there's a feel to it. Very light cuts and very heavy cuts are both bad. Depth of cut, cutting speed and feed rate matter. And what's possible is probably limited by a hobby machine, making this a skill. My mistake was being too gentle. Rubbing heats up tools and blunts them. In contrast, when a proper cut is taken much of the heat is carried away by the swarf.
4. Clear swarf enthusiastically. Chopping swarf under the edge murders tools!
5. Cooling and lubrication. HSS and carbide are different. For many small jobs with Carbide I don't bother. HSS benefits more. There is a range of jobs where dabbing and splashing help. For heavy work like cutting T-slots I use flood cooling: it removes heat and swarf efficiently. Aluminium needs special care because it has a low melting point and can stick to the tool.
6. Fitting the tool to the job. Very cheap tools may not be much good, top range tools are far too expensive. Finding the balance is tricky. I don't see much point in wasting money on tools that will last longer than I do! Others have good reasons for investing solid cash in high-end machines and tooling.

It would be an interesting experiment for Ron to repeat the job with a new cutter from the same source. I suspect Ron's second attempt would leave the cutter in better condition, simply because Ron learned so much from his first attempt, perhaps without realising it.

I'm a great believer in theory and book learning but there's no substitute for actually doing it!

Dave

Edited By SillyOldDuffer on 02/01/2019 10:18:55

There is still a lot to learn Andrew, just annoyed with myself when I dont think things through, I would like to think that I usually do but I obviously didnt in this case.

Ron.

Dave,

I will do a test with the same tool, I have just looked at it and it maybe ok, I was just asking too much of it.

Ron

If you milled the 8mm slot past full depth first then it would be possible to make a small single edge cutting tool with a piece of HSS (even an old milling cutter that can be repurposed when at the end of its normal life). Rough out something like Ø14mm x 6mm deep knowing you have an easily sharpenable tool that does not need to be pretty or an exact size then clean up to size with the tee slot cutter.

Martin C

Well all is not lost despite my iffy start, I put a small block of 6082 up and cut a 8 mm full depth (+2mm) slot. Then turned the speed up to 750 rpm and tried the T cutter, it seemed to cut ok and obviously a lot easier to feed in then the slots I cut on the table plate. If I did take the edge off the tool it cant be too blunt as it cut ok second time around.

I,ve done the second mod to the mill, in a way quite a major mod as the mill now has reverse yet it is so simple to do.

The small board in behind the mains switch has a small 3 pin connector sitting empty. The male end of a R/C servo lead fits it perfectly, this is connected to a single pole two way on/on switch and thats it job done, forward and reverse.

Another mod to the mill, fitted a spindle speed DRO. Easy to do, just a bit of metal work to mount the sensor, I thought of making a mount for the small round sensor magnet but it is really strong and shows no sign of movement even at full speed. I wasnt going to bother with a speed DRO and despite the high cost I decided to fit one, total cost £6.70 

Edited By Ron Laden on 05/01/2019 10:32:02

Forgot to say that the 3 mods I have done so far, the gas strut, the reverse running and the spindle DRO are all taken from the Howard Winwood review on the SX2P.

Well worth a read for anyone with the SX2P or for anyone considering one, you can find it on ARC,s website. There is a link to it under "more" along side the mills specification. He also covers fitting DRO,s for the mills 3 axis.

Ron

One of the reasons I fitted the switch and enabled the reverse was to give me machine tapping so I gave it a try and it seemed to work fine. It was a bit awkward reaching around the camera but I tried a couple of M6 threads in some 6082. Since fitting the gas strut the head is nicely balanced and it took very little pressure to keep the head feed in front of the tap (if you see what I mean). The good thing is, the mill stops almost instantly from low revs so its quite controllable for tapping.

The alu test piece is quite thick at 38mm but they were through holes and it will probably be a bit trickier with blind holes. I will have to think of a method to prevent bottoming out the tap but I guess something as simple as a piece of tape on the tap as an indicator allowing me to stop plus a bit before the bottom of the hole would work.

Ron

Edited By Ron Laden on 11/01/2019 14:32:59

I have changed the gas strut on the mill from a 220mm stroke to a 300mm which has recovered the full head travel from top of column to its lowest position. It meant making an extension bracket to mount the top of the strut and I used a piece of 20 x 10mm steel bar. It worked out quite well as I used the M10 hole in the side of the head which was left over from removing the original spring/lever assy. I also removed the head handle M6 end float adjusting grub and replaced it with a hex head and locknut as the second mount, so no drilling and tapping just used existing holes.

I may never use the lowest position but its good to know its there for anything shallow fixed to the table and the 50mm lost at the bottom with the 220 strut is available again.

A bit awkward to photograph but the M10 hex is at the bottom of the pic with the M6 close to the cable conduit.

Excellent mods Ron, especially like the power tapping.

Emgee

Emgee

The mods are simple to do, low cost and make a real difference so I think well worth doing.

Ron

Edited By Ron Laden on 03/03/2019 16:40:06

I have a small job coming up for a friend which needs a number of 1.0mm x 5.0mm deep slots in a block of aluminium and I immediately thought of a slitting saw. I have no experience of them but as well as this job it could be a useful addition to the tooling.

Looking in the ARC catalogue I see they do a range of sizes of arbors and saw blades, I was thinking maybe the 16mm arbor which has an o/d of 27mm and 63mm diameter blades which would give a cut depth of 18mm. The next size up is the 22mm arbor which I guesstimate would have an o/d of 33-34mm it uses 80mm dia blades giving a cut of around 23mm.

Having never used one and not knowing what jobs or depth of cuts will crop up I am wondering as a starting point which size to go with, any thoughts would be appreciated..?

Ron

22mm would also suit metric gear cutters if you need them for your Traction Engine.