Member postings for Andrew Johnston

Using a backplate allows one chuck to be used on many different designs of lathe. Only the backplate needs to change. If the chuck body is threaded then it severely limits the number lathes that the chuck will fit.

Andrew

If by an inverter the OP means a VFD as a replacement for a converter there are a number of issues.

One, the output of a VFD is PWM where the pulse width changes every pulse so that the fundamental is a sine wave. Running PWM waveforms around the workshop without proper shielding could cause all sorts of interence problems. Filters are available to filter out the higher frequencies. They are conceptually simple, but are expensive as they are carrying full load currents.

Two, VFDs have a number of internal parameters that are tied to a motor specification. The parameters provide soft start and overload protection among other features. Not tying these parameters to individual motors may cause problems.

Three, VFD outputs do not like being switched when running, it's an easy way to let out the magic smoke.

I'd either try and fix the existing converter or swallow hard and install proper 3-phase. I did the latter and am glad I did so. I connect up my machines and they just run, as does all the control gear. So I can get on and make parts not faff around with electrics.

Andrew

Personally I'd go with 90° inserts. That way you can mill close to, or all the way up to a shoulder. With 45° inserts you can only mill on a flat face and considerable clearance is needed all round.

Rigidity is relative; I consider my Bridgeport to be flexible in more than one sense. Whereas my horizontal is pretty rigid. See here for some results on the horizontal using a 63mm diameter face mill from Arc:

Face Milling Results

Andrew

Maximum I run on my Bridgeport is 50mm diameter and that is power limited to small DOC. On the horizontal mill I run 63mm and 80mm but that is a much bigger mill; 5hp and 3500lbs, so one can take proper cuts in terms of depth and feedrate. Face mills are all about removing material as quickly as possible.

Andrew

I'm pretty sure they are screw on extension pieces. I think I have one somewhere, but have never tried it.

Andrew

Could be that the spindle is fine but the test bar is not seating properly in the headstock taper.

Andrew

Tapping and clearance sizes for the smaller UNC and UNF threads.

Andrew

When i drilled the holes for fixing the smokebox to the boiler I drilled the holes in the smokebox using the rotary table. I then picked up on each hole with a magdrill and drilled through. Of course I have steel boilers. They weigh close on 100kg so are way to big and heavy for me to manhandle onto the vertical mill.

When I get around to the cylinder mounting i will drill the holes in the cylinder flange on the vertical mill using an angle plate to set the angle for each hole. The holes will be oversize to allow for the cylinder being pulled down onto the gasket. Once I am happy with the cylinder position I'll make a silver steel punch and spot punch through each hole. Then I'll pick up on each location with a pointer in the magdrill chuck. Exact positioning isn't critical. Clearances need to be quite large to ensure the cylinder sits down properly rather than binding on the studs.

Andrew

On my Pultra 1750 all the dials are marked 0 to 100 and the screws are 6mm diameter and 1mm pitch. Possibly 0BA as other threads and screws are BA. I doubt spares are available, but shouldn't be difficult to make a new one.

Andrew

+1 - that's the proper engineering approach.

Starting right at the beginning can we assume that the lathe still has a 3-phase motor? If so, and you don't have a 3-phase supply, how is the motor being driven?

Andrew

Wow!

Andrew

Update: Rather to my surprise I got a letter from the DWP today telling me what my state pension would be, every four weeks. It is exactly four times the forecast value on the HMRC website. As a result I am now 100% confident that the COPS estimate on the HMRC website does not affect the forecast pension value, thus neatly answering my original question.

Once I have sorted out a disagreement with my accountant over my capital gains liability I will be paying the NI due for the tax year that ended in April 2022. That will give me an extra £5.29p a week on the state pension.

Thank you to those who have taken the trouble to reply to my original posting. It's been interesting to read, if pensions can be said to be interesting, important, yes, but interesting?

Andrew

Although not explicit I assume it is implicit that all voltages are phase to phase. In theory running 415V star or 240V delta shouldn't make a difference. There might be a small advantage in using star as the lower currents might result in lower resistive losses.

Andrew

The drawings for my engines called for a 2-start 1/2" pitch, 1" lead worm and a mating spur gear but with teeth on a slant. However, the dimensions didn't add up and information was lacking, so I re-designed, sticking with a 2-start worm. My lathe will cut a 2tpi thread, but not 1tpi. So I decided to use the CNC mill to make the worm. On another forum it was pointed out that a 2-start worm will back drive. So I changed the design to single start and also a single enveloping worm wheel to match full size. I stayed with using the CNC mill for the worm, as I was concerned about using the lathe to cut an Acme full form 2tpi thread; the lathe leadscrew is 4tpi.

The worm was roughed out using 6mm and 4mm end mills and finished with a 15 degree (half angle) tapered commercial endmill:

A similar process was used to make a hob from silver steel:

The worm wheel was gashed and then free hobbed:

The dividing head is used to gash the worm wheel but plays no part in the free hobbing. The worm wheel is free to spin on the arbor.

Of course the above is all rather long winded, but I was interested in the design process, and to see if I could make a matching worm and worm wheel.

Andrew

Provided the original question doesn't get lost I am happy with thread drift. You never know where it will lead. So it can be interesting and informative.

Andrew

Just spoken to my Hobbyweld agent; saying 10 weeks for acetylene. Being realistic that means next year. I'll have to postpone flanging the tender sides for my traction engines and work on something else.

Andrew

Above 50Hz the VFD/motor combination should be constant power. As the frequency increases above base frequency (50Hz) the phase currents, and torque, go down as there isn't enough voltage to maintain the currents. But the speed increases. The decreasing torque and increasing speed cancel out, giving constant power.

Andrew

In general single start is prototypical; anything else will back drive. On my engines I threw the drawings away and designed my own single start worm and worm wheel. On my 4" engine the worm is 1.5" OD, so 1/2" seems a little small for 1.5" scale. Can't help with the screwcutting as I CNC milled my worm. These are finished gears:

Andrew

Thank you to all those who have replied. It has been helpful, and interesting. I think we can safely say that the UK pension system is grossly over-complicated and few people, let alone the government, understand it!. In the past I was an employee elected pension trustee and I still don't really understand pensions.

What I understand from the replies is that the estimated state pension value given is what you will get, give or take small changes due to circumstances. That is what I would have hoped.

I turn 66 early next year and will be taking the state pension as soon as I can. I am slightly niggled that although I have 48 years ot NI contributions, assuming I pay up for the tax year ending last April, I will still not get the full state pension. I will be about £6 a week short. I've only missed two years since leaving school, while I was doing my Ph.D. It is interesting that my NI record says I have three full years prior to 1975, which is when I left school. Those years must have been due to summer jobs, one year at the Texas Instruments plant in Bedford and two years at RAE Bedford. As far as I can see I am unable to make any additional NI payments to get the last six quid or so per week. All my years, apart from the two missed, are full.

I started getting my university pension earlier this year. It just about covers the council tax, but is a defined benefit scheme and is index linked. I've moved around a lot in my career, so pensions have been all over the place, and I have been self-employed for a lot of the last 20 years. But I am fortunate to have a couple of substantial defined contribution personal pension funds, plus investments, so I shouldn't be living on the streets, at least for a while.

Andrew

The trouble with running a VFD below 50Hz is that they have a tendency to keep phase currents, and hence torque, constant. Since power is torque times velocity as the velocity decreases, but torque stays contant, the power also decreases. Given the motor is only 1/2hp it really needs to be putting out a 1/2hp.

Andrew