Member postings for Kevin Cobley

Hi - sorry my recollection was way off. The holding face measures ~7.5 - 8mm long on the 6mm collet made from the blank. Apologies for fading grey matter !

Regardless, it seems like a smaller cutter is the order of the day.

Thanks for the guidance.

Sure I understand what you are saying. I ought to go and actually measure it rather than recollecting from my work office. But sure, its starting to seem that smaller cutters are in order. I have a 3mm shank cutter already so I shall see how that fares. I have a normal collet for that diameter as well.

OK, I see what you mean - maybe running a smaller cutter and making more passes is the right approach. The closing force is then spread over a smaller area.

As an area thing, then it would scale by the square, so easy to get rapidly into trouble.

I could be pushing it too hard - yes - I guess I'm still finding out what I can get away with. Yes its for small stuff - I think it was originally bought for the war effort machining bomb fuses. But even when doing light surfacing, I found I had trouble. Hence checking if I'm being too ginger with the collets.

So I had a look at the calculations - wasn't too painful:

R8 is 7/16 - 20TPI and has a mouth angle of 16.5deg - 7/16th is 11.1mm

Pultra 10mm is 9.886mm x 1mm and has a 30 degree mouth angle

So apart from the mouth angle, the puller is similar. If we calculate the pull force from the torque as T=cDF, where D is the diameter of the thread, and F is the pull force, c is the coefficient of friction (0.2 for steel)

firstly: 30 -35 ft-lb == 40-47Nm (I prefer to calculate in metric, just for unit consistency sake - easier for me)

At the lighter end this is 18kN pull force, and thus 64kN holding force through 16.5deg

For that holding force on Pultra we would need a torque of 32Nm, which is a lot more torque than hand applied.

so 32-37Nm which is 24-27 ft lbs.

Human hand max torque is typ about 18NM according to NASA, so I would need to add a lever to the hand wheel to achieve this.

So the question then remains whether this is acceptable torque on that collet system, but at least I know that I expect trouble with just the hand tighten force.

Thanks for the thorough response - I think I'll skip the matrices, at least for now

I will get the calculator out and work out you 30-35ft/lb R8 numbers and go on the odyssey of converting the numbers to my p9 - it will at lest give a ball park!

Your BCA is not a dissimilar size to my Hauser - I have 4" X 3"Y and 2 3/8" Z travel, but it was advertised as a milling machine I think its a 33B (not that they seem ever to have made 2 machines the same..)

I'll be back, in the word of a famous android..

Kevin.

I should add drilled and reamed to 6mm, btw

To be fair, the collet is not a dead hard collet in this case, but a machinable blank that has been drilled to 6mm and slitted, so the collet is definitely softer than the cutter which is carbide.

The collet holds at the nose, but the length of the holding section is not very long - maybe a couple of mm?

The nose internal angle? Not sure there is one. These collets seem to have a gripping range of like +/- 0.1mm.

As for comparisons - I havent done a comparison. The Lathe seems less of an issue since the work is held and the cutter is a point tool, so there is little longitudinal force on the work. Its spiral end-mills pulling as the cut on the side faces or pushing as the cut on the bottom that are the problem.

I was trying to be cautious but I have no idea what the limit is. If I tighten up the collet, then its OK, but am I over-tightening it? I have no feel.

I have two machines that take 10mm Pultra collets, one a 1750 lather, and the other a Hauser Mill.

On the lathe, its not a big issue, but on the mill I have trouble with end-mills getting drawn from or pushed in to the collet.

I can't find a recommended closing torque mentioned anywhere for this collet system. Does anyone have some info or experience?

The mill has a knurled hand wheel for the collet closer and I'm nervous of using more than hand tightness on this. It does have holes that may be for a pin wrench or tommy bar of some type, but I really don't want to wreck the threads on my collets or draw-bar..

Many thanks,

Kevin.

Unfortunately, as Martin suspected, the motor only has three studs in the connection box, no star point. So this would make a VFD un-economical , I think. This is kind of where I came in.

Thanks for the taperlock link. In this case it'd be going from 14mm to 5/8ths, so I don't think there will be space as their OD is 35mm unless I've misunderstood how they're meant to work.

I need to get some photos for you all..

With regards to safety devices - more for my forgetfulness. If I turn off the switch at the wall, then I don't want the meachine to suddenly energise when I switch on the plug. Also my teenage children are sometimes admitted to the workshop, so they can get to see how real stuff actually can be made etc.

An EMC can be an issue - a friend of mine fitted a chinese VFD to his lathe only to discover that the electronic LED light controller next door went completely haywire when he used it - he described it as a lathe controlled disco light. His neighbors were not impressed - inside there was no filtering on input or output - this is how they undercut the competition. Still had all the badges, but ofc just meaningless.

Anyway - sounds like an older cap start motor with centrifugal switch is what I need to find then.

Next thing to sort out on it is how to get the gear lever off - the short taper pin is stuck tight and I cant clearly tell which end is which..

Thanks forasking about the voltage - the label states 415-440V so it would need a step up VFD.

This model drill press has back gear for slow speeds, so could be used for tapping etc, which is why it has reverse.

Yes a zero volt switch will be added and also an emergency stop. It has neither at the moment.

I'm curious about these £100 inverters. Whenever I looked they were much more expensive than that, at least for reputable brands. Some of the cheapo ones have very bad EMC, and what looks like inadequate heatsinking. If you can point to a good model at £100 then maybe its worth it, but from what I see a single phase motor will cost less.

Thanks for the sizing information. I checked and mine is 3in. by 5in. which doesn't fit any of those sizes. So it looks like something older is the only way? Any good places to look other than the usual auction site?

Yes, ofc, forgot to mention that the original motor is 3/4HP (550W in modern parlance). It has the foot type of mounting that seem fairly universal - 3 inch wide, four screws.

The Pulley doesn't really have any meat for boring out, especially for 19mm shaft. Hadnt considered turning down the shaft of the motor - interesting.

Contactors? Don't think I have any of those. The drill press has a rotary switch -off-forward-off-reverse- Internally it has a 2-pole changeover and a single pole on off, so I suspect it can be used to reverse a start winding if the motor has a centrifugal switch.

Re-reading my post, I ought to mention that I'm expecting to replace the motor entirely, not re-use the 3-phase motor.. so easy to miss the obviously required info

Hi,

I have recently acquired an Elliott 2GS Pillar Drill, which I need to convert from 3 phase to single phase. Whilst I understand a fair bit about how motors work, I'm still not sure what my options are regarding start capacitors and switch-gear etc.

The machine has a built in forward / reverse changeover switch which ideally I would like to continue to use. What's the usual practice for this type of replacement - do I need a motor with centrifugal switch - can I avoid any further switch-gear to start the motor?

Given that the pulley is 5/8th diameter shaft mounting, I suspect I may be limited to older motors as new ones seem all to be 14mm or 19mm shaft diameter.

Thanks for any advice,

Kevin.

Not sure I understand your thrust, Howard. Ten years ago I tried to take up a course but it kept being cancelled and then the course died altogether. I have done a fair bit of turning, at school and on my engineering degree, so coming back to it nearly 30 years later I started off by resisting the urge to dive in and deciding to work through the a-fore mentioned book. I don't think I'm 'rushing' in. These days one has to rely on youtube and the kind assistance of folk on the forums.

The milling machine I bought is small enough for my space, and cost less than modern machines of a similar spec, but is clearly made to do the job properly, unlike many modern machines. It doesn't need refurbishing - its in very good shape with little wear and having obviously been looked after. My target projects are small stuff to which its well suited. What else would you suggest? I don't hanker for a bridgeport.

What I don't have is a cupboard full of tooling. The lathe course assumes you have all manner of accesories, for instance, like a fixed steady, and drilling jigs or vertical slides - my lathe happens to be fairly well provisioned, so I was OK*. The Mill came mostly bare, so I'm starting to acquire a vice and need a workholding kit and some cutters. I'd like to start by making more stops for it, for instance - not too ambitious.

So I started with a clamping kit on my shopping list but came unstuck immediately, hence the post. Others have explained that this is normal - thats understood, and now my first project will be some t-nuts. Whats the issue?

Kevin.

* my lathe came to me via a friend at a price that was a bargain. But the lathe has been 'tinkered' with extensively, presenting its own challenges. The fixed steady for instance, has bearings attached - their hard shells marr the work - lesson learned - mod. will be removed before I use it again. There are a number of other strange things about it that I have to work around, like the boring out of the spindle to accept 2c rivett collets which means it no longer has an MT, which could be lived with if the collet nose had not been lost at some point...

Edited By Kevin Cobley on 21/02/2021 16:03:41

I'm sure thats right, but the lathe course leads you down paths in the first project that are not well thought out. The fly cutting arrangement was to clamp the workpiece against a slot in a vertical plate clamped to the cross slide. My machine already came with such a drilling jig. The book shows a small engineer's clamp holding the work against the slot, and you are required to fly cut to within 10mm of the base, so the clamp size is determined - it looked dodgy to me, but then thats what the course asked for.

The result was that the fly cutter just rotated the work in the slot even on a very gentle cut. I tightened the clamp as tight as I dared and tried again, and the result was the same, even with a tiny cut. It just doesn't work. Had to resort to a hand file to clean up the mess made.

Starting off by putting the student into the realms of questionable practice is not a great way to inspire confidence.

Edited By Kevin Cobley on 21/02/2021 14:24:53

I have a couple of these - the lathe basics and the lathe course. The lathe course was not great, so far - some of the clamping arrangements were risky (e.g. for fly cutting in the lathe) and key bits of info glossed over at points - I guessed I learnt what doesnt work in a few places..

For the price, I may get the milling course too. I do have lots to learn, though I suspect my mill is too unusual for the book - might have to scale everything down

Sadly, not practical on my little mill as it only has one slot in each axis. But I get the general idea.

As I'm getting a clamping set that comes with standard t-nuts for the mill, I may as well take the file to a couple of those to get me started - should be easy enough and there would be no need to worry about squareness as the top surface and threaded hole would be intact. Would only need to file the bottom and the sides of the spigot.

Had wondered about the stud going thru - makes sense to stop that with the staking

Photo of Hauser Mill

Edited By Kevin Cobley on 21/02/2021 13:47:16