Member postings for Andrew Johnston

Interesting finish! Is the surface smooth to the touch or is it rough and the surface torn? I have seen this sort of smeary finish before. It could be the material, the insert or speeds and feeds. One thing it isn't likely to be is the lathe. At this stage I'd guess speeds (too low) and feeds combined with a sticky material. What speed and feed were used?

Andrew

This is the pump unit:

Looks to be complete, but never used. A possible issue is the motor is 3-phase and looks like it is configured for star only, without digging into the motor.

Your copy attachment looks almost identical to mine, albeit with some parts missing. Right side of mine:

The obvious bit missing is the toolpost, although this is a self-contained unit attached by three screws (3/16" BSW I think). So it could be replaced with a home brew toolpost. The bent handle for the indexing stop is missing as is the adjustable stop on the body. But neither of those would be difficult to make. Left side of mine:

Looks to be the same as mine, nothing missing. I've never worked out what the coarse adjustment stop on the left side is for. Unless it an "oh s**t" stop that provided a last chance stop if, for instance, the follower misses the pattern.

An obvious question is where are you based, I'm near Cambridge.

Andrew

Comments above.

Andrew

The requirements versus budget is utterly unrealistic. The only way to come close would be an ex-industrial machine, but that has been discounted. By greatly reducing the requirements the budget could be met, but no way are 98% of the requirements going to be met within budget, especially spindle bore.

Andrew

I've just measured on of my 6BA screws and the OD is 0.108", so only 2 thou under nominal. But my screw was bought from EKP (in the UK) so it's a cut thread, not rolled like most commercial screws. So I'd bet it's 6BA.

Andrew

Finished my batch of 3/8" BSPT blowdown plugs:

At the top are a couple of embryo fusible plugs for a member of another forum, whose lathe will not cut 19 tpi threads. The gauge line on the blowdown plugs is pretty consistent from plug to plug. Given the shallow taper I estimate that the diameter at the gauge line is less than a thou across the set. Pretty pleased with that, especially given my previous hiccups with the hydraulic copy attachment trying to get consistent results.

So many jobs lined up I'm not sure what to do next. Even when the lockdown is downgraded looking for subbies is not going to be a priority for most companies. So I've probably got another couple of months at least of thumb twiddling to go.

Andrew

I haven't used any standard Glanze holders, but I do have several of their boring bars. They seem pretty good to me, but the supplied inserts were rubbish and were duly binned. I use Korloy CCMT and CCGT inserts as standard.

Brass should be fairly easy to turn. But aluminium and especially steel can be a real problem if you don't know the grade. Many low carbon steels are sticky and can be problematic when turning with inserts. I'd get known materials to experiment with, 6082 for aluminium and EN1A for steel.

If you have a bench grinder you could also try HSS tooling. It can be more forgiving of speeds and feeds than inserts.

Andrew

Not brillant. I haven't measured all four corners on the fixed jaw on my vice but I have measured the two top corners. I couldn't tell the difference with a tenths micrometer. So less than a tenth variation. But the vice was a tad more expensive.

I measured the jaw as I don't use keys but indicate the vice each time I move it. It's convenient to use the back face of the fixed jaw but I wanted to know how it related to the side that mates with the work.

Andrew

First question; have you ever got a good finish when turning on any other lathe? If the answer is no, or you haven't used another lathe, I'd be looking at the tooling and material before blaming the lathe. Is the tooling HSS or insert, and if inserts what type and where from? What grade is the material? Material of noideaium grade are generally not good.

Andrew

I don't use dies very much, preferring to screwcut or use Coventry dieheads. But oddly enough I've just cut a 5/16" BSW thread in EN8 as I didn't have the appropriate insert for screwcutting. Rather to my surprise I managed a really nice thread. I turned to nominal diameter. I held the die in a tailstock holder from Arc. I started the thread by turning the chuck by hand while applying force from the tailstock handle. The die was secondhand from Ebay many moons ago. I think it's the first time I've used it. The important point is that it was a quality die, HSS ground thread by Warrior.

Andrew

When running an induction motor from a simple VFD the torque does not decrease as the speed decreases. It will stay approximately constant. But since the speed is decreasing, at constant torque, the power decreases in proportion to the speed decrease. Simples!

Andrew

The only time I've seen frizzy blue swarf like that shown was when turning hardened silver steel with a CBN insert. The turning was done at high speed, shallow DOC and a high feedrate. The swarf was also very brittle.

Andrew

Don't knock it, a good finish is a good finish no matter how it was obtained.

I suspect part of the issue may be that the tailstock centre allowed the pipe to flex slightly compared to the chuck end. Schedule 80 refers to the pipe size but not the material. I'd guess it's a low carbon steel and hence might be sticky. The key to machining sticky steels with inserts is high surface speed, as discovered.

Andrew

Yep, but designed by Dogbert not Dilbert, who's far too smart to actually finish anything, or stay with a project to the end.

Cynical wot me?

Andrew

I have a spare tank and pump that might be available. I've never used it so I don't know if it works, but it doesn't look in bad shape.

IIRC the system runs at about 350psi, much more than that would result in things going pop.

Andrew

Indeed it is a 3-flute cutter, because that's what I had. As stated above fewer flutes are good for soft materials, not so much due to depth of cut but to higher chip loads so more metal removed per revolution. I use mostly 3 and 4 flute cutters as a compromise. For HSS it doesn't matter how many flutes, just adjust the feedrate to suit.

Carbide inserts for lathes often perform better at high surface speeds. The same is not true of carbide milling cutters. Professional grade carbide cutters are much sharper than the old HSS cutters. There are some coatings that require high temperatures, and hence high speeds, to work properly. But I suspect most of us don't have mills capable of making full use of some of the more estoteric coatings.

I was running the cutter at 3000rpm and 200mm/min and a stepdown of 0.5mm. The key to milling and turning hardened steel is to get the shear zone red hot and soft. So than means shallow depth of cut but high feedrates and reasonably fast speeds.

Andrew

Do you mean the tank and pump for the hydraulic oil?

Andrew

Edited By Andrew Johnston on 01/05/2020 15:55:01

Correct, it's possible to mill HSS with carbide tooling:

If I were doing this I'd make an involute cutter, like this cutter for splines, but smaller:

Andrew

It is indeed the correct patent. Thanks very much for posting. Thanks to the patent I've been able to get the micrometer adjustment working in the way I expect. Tomorrow I'll give it a go when I make another tapered thread plug.

Note that I said I've got it to work, I'm still not sure how it works. I'll have to sit down and study the patent. The trouble with patents is that they're written in a stylised way such that everything needing to be patented is described but in such a way as to make it difficult for others to understand and implement.

It's interesting that the patent is dated 1971, not long before the attachments were rendered obsolete by CNC lathes.

Andrew

Made, and fitted, a new toolpost clamp for my hydraulic copy unit from EN8. I also worked out how to use the micrometer adjustment feature from information kindly supplied on this forum. Tomorrow I'll have another go at making a tapered plug and see if I can get the gauge line in the right place this time.

Andrew