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Member postings for Mick Dobson

Here is a list of all the postings Mick Dobson has made in our forums. Click on a thread name to jump to the thread.

Thread: What lathes have you had?
22/07/2019 12:34:28

Unimat SL. Got this about 1981, still going strong. I made a high level tailstock and raising block for the headstock for larger jobs when needed. But normally use as standard.

Myford ML4. For a couple of years.

Myford ML7B. Great machine and quite versatile, surprising what these will do as long as they are decent condition.

Chester Coventry gearhead (same as a Warco 1332), bought new in 1997. This is a green Chester, before they changed colour to grey. My main lathe and very good at most things. But not Colchester or Harrison quality.

Myford ML7 Trileva and Portass Dreadnought , bought as a job lot.

I sold the Trileva and the original ML7B and kept the Portass Dreadnought instead. All the main parts have the maker's stamp identifier. I made a longer cross slide for this as well as a new set up for the motor and countershaft. Also modified the headstock to a Myford nose register so that popular accessories will fit.

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Thread: Warco Super Major Mill
31/01/2019 12:30:46

I bought a Super Major in 2008 at the Harrogate show. I would say it is a very good machine for the price, which back then was probably better value than it might be at today's rates. I added a DRO to X and Y on the table and Z on the spindle.

One or two problems over the years. The biggest issue I have had is the table traverse gearbox broke up at the engagement mechanism after a few years. I replaced it with a home made system.

The spindle lock lever is a bit flimsy and can spin on the shaft so I machined and welded on a hex piece so that I can lock it with a spanner - much better. The gearbox is a bit noisy, especially at the top speed, just use decent 68 grade hydraulic oil.

My previous mill was a Warco Minor with a round column, so the Super Major with dovetail on the vertical travel is a real bonus.

Thread: Traction Engine (Electric)
22/10/2018 12:40:55

One of the reasons for having a traction engine run off an electric motor and battery power is that there won't be a need for a boiler certificate!

I started building a 2" scale Fowler ploughing engine to the John Haining design about 21 years ago and the first thing I did was the boiler. I had it welded in steel, a really nice job by a chap in the local engineering works. However not all of the plate material was traceable and neither was the welder's coded credentials. Oh dear!

Two house moves later and the job has remained stalled ever since. My plan now is to incorporate a dc motor and gearbox in the boiler shell and connect that to the crank drive above. The boiler tubes never got finished anyway so basically there is an empty shell to work in. The batteries would go in the driver's seat carriage.

It's still a job for the future (retirement?) but definitely on the 'to-do' list. Working on at least two other major projects before that.

Thread: Let's hear it for British manufacturing!
06/08/2018 12:24:17

Triumph motorcycles from Hinckley.

Well, at least for the first 10 years or so of production. They seem to have lost some of the individual 'Britishness' now, but still high quality desirable machines.

I have a '93 Trident, but normally ride my '93 Moto Guzzi.

Regards,

Mick

Thread: Alba 1A Shaper.
29/05/2018 12:39:37

I picked up an Elliott 18M shaper a couple,of year ago when a neighbour's father closed down his engineering business for retirement. Not exactly 'picked up' as such, since it has an enormous weight!

I managed to get it home and off a sturdy 4 wheel trailer behind my Volvo Amazon then somehow got it into the workshop. I made some steel plates to bolt under the machine with very HD castor wheels so that it can be moved around. It now sits on sturdy wooden blocks with the castors just off the floor. I also replaced the 3 phase 4hp motor with a single phase 2 hp. More than enough power for what I do with it.

I may fit one or two more e-stop buttons in various places around the machine, just in case.Treat a shaper with respect, they take no prisoners. I really enjoy using it and it has been very useful in updating the Portass Dreadnought lathe with a better cross side and a front and rear toolpost.

Regards, Mick

Thread: PORTASS LATHE
15/05/2018 12:43:48

My Portass is a Dreadnought, which is a similar lathe to your PD5. I modified the head stock spindle to that of a Myford thread form so that other attachments readily available for Myfords will fit the Portass.

For ER collets I have a spindle mounted screw-on adaptor. So there is no need for the draw bar and I can hold longer items through the collet.

Thread: Advice on Belt Tensioners
12/04/2018 22:04:12

I used a Volvo Amazon handbrake lever with ratchet mechanism as a belt tensioner on my Portass Dreadnought lathe. The motor is fixed to a sturdy plate hinged at the back of the lathe. Easy to set the belt tension and lets me change speed on the go without starting and stopping the motor.

Regards,

Mick

dsc00474.jpg

Thread: Motor control for Shaper machine
27/12/2015 19:41:47

Hello all,

I picked up an Elliott 18M shaper some 12 months ago but have only just got around to look at setting it up to use.

The motor is a Brook Crompton 400V 3 phase, marked as 4 hp and 1400 rpm. My workshop only has single phase, although there is a 40 amp outlet on the fuse box. I use this to run my 2hp lathe and my compressor, when needed.

So my immediate choice is, do I swap the motor for a single phase type or go the VFD route and stick with the 3 phase motor?

If I go single phase I reckon a 3hp motor would suffice, I won't be taking half inch cuts for my purposes, even if the machine is a brute of a thing! It may involve some engineering mods to adapt the drive pulley and fit the motor to the mounting bracket, otherwise should be reasonably straight forward. The down side may be less smooth running, but is this so critical on a shaper?

If I stick with the 3 phase motor, which VFD to buy? There are some tempting prices on those Huanyang VFDs on ebay, but are they any good? Is it a case of you get what you pay for? European and Japanese VFDs to handle 4 hp seem a bit juicy in terms of cost. Much cheaper to buy a single phase motor?

The shaper has a clutch, so VFD feature of creep control not so crucial.

Anyone done this before? All suggestions welcome.

Regards, Mick

Thread: supercharged V12 2 stroke
02/12/2014 12:38:57
Posted by Howard Lewis on 09/10/2014 21:57:59:

The Fairbanks Morse, Napier Deltic, Rolls Royce K Range, and Leyland L10 engines were all opposed piston two stroke diesels. The Deltic had three banks of six cylinders, operating three crankshafts, which were interconnected by a geartrain at the front of each bank.

An excellent sumary of 2 stroke engines by Howard, as used in industrial, automotive and marine applications.

Just a quick note (as an ex-Leyland test engineer), the Leyland engine was designated L60. It was developed primarily for use in battle tanks. The L10 was a more recent Cummins truck engine of 10 litres, a conventional 4 stroke and nothing to do with Leyland.

Dean, always look forward to seeing the latest update on this amazing build.

Regards, Mick

Thread: Fly Cutter Milling Speed?
24/04/2014 12:16:34

Hello Jon, yes seems about right as a first go. I would normally base mild steel at 80 feet/ min, giving a cutter speed of about 150 rev/min at 2" diameter.

Not sure if your mill is a "model engineering machine" size, in which case err on the lower speed and work up until it seems right. Depth of cut and feed rate will play a part also. The more rigid the machine and set up, the more you can push the depth of cut and speed.

Regards,

Mick

Thread: Tensile Strength - Brass or Bronze?
22/04/2014 18:03:26

"If it's the strength you need it is not the tensile, but the shear strength your looking for"

Both tensile and shear really; with a load applied somewhere along the foot peg, there will be a shear force at the fixing point (bolt or stud in the end of the peg) plus a bending moment (couple) acting about that point. So the foot peg could bend along it's length and /or shear at the fixing. I expect the weakest point will be the fixing bolt, not the footpeg, unless it is made very thin walled.

As mentioned, price could be the limiting factor, not material strength!

Mick.

22/04/2014 12:21:19

Brass (70Cu/30Zn) has the higher tensile strength at 550MPa, compared to Bronze (90Cu/10Sn) at 260MPa.

Therefore would seem brass is the preferred option. Easier to polish up too, and cheaper no doubt.

Thread: dro encoders
31/01/2014 14:51:29

dsc00601.jpgdsc00600.jpgHere's another take on installing a cross slide DRO to a GH1330 lathe. (Actually it's not a Warco, but a 1997 spec Chester of the same type, when they were painted green and before they started selling the grey paint spec machines. Has been a good machine.)

My method has the DRO situated beyond the end of the cross slide. It enables the tailstock to still be moved right up to the back of the saddle, also it keeps the DRO working parts well away from swarf and coolant.

The long plate extension screwed to the top of the cross slide supports the DRO scale, which effectively moves with the cross slide. The DRO pick up comprising the wiring lead is fixed to a bracket projecting from the back of the saddle. It has proved to be a highly effective and very rigid set up.

The only downside is that I had to move the lathe slightly further away from the wall and also modify the rear splash guard to suit.

For issues on lathes where the cross slide gib adjustment screws would be compromised, situating the DRO at the end like this would solve that problem too.

On the saddle DRO, mine too is at the back, like that shown on Coalburner's lathe. I added a further swarf guard above the DRO body as a second line of defence, although the DRO seal strip is at the underside anyway so should be fine.dsc00597.jpg

Regards, Mick

Thread: warco Major gh miller
27/01/2014 20:00:15

Hello Brian,

I have the Super Major, which is the version with the dove-tailed vertical column, as opposed (I think) to the round column of the GH Major. I have been very pleased with it in general. The only issues are that the gearing can be a bit noisy (experiment with oils) and also when the fine down feed quill drive is engaged, the main hand levers at the side can tend to jump back into mesh and this causes the quill to then retract to the top. I solved this by hooking a light elastic band around the levers when in fine quill feed.

I fitted DROs to the table on X and Y travels, and also to the quill Z axis. invaluable enhancement! My machine has the powered X travel and this motor too is a bit noisy. I make sure the gearing is well greased and not too tight in mesh.

Overall, a good machine. My previous Warco Minor was a good 'un too.

Regards, Mick

Thread: Combustion chamber temperature
20/01/2014 17:55:19

I should explain, the 900C is the gas temperature, not the cylinder head or valve seat materials.

A good estimate of max temperature of the exhaust valve seat is 350C. Also, the seat will normally expand more than the surrounding material so should remain tight. I would go for a light interference fit of approximately 0.001" to 0.002". However if bonding agents can be found that are good to say 450C then this could be worth a try.

Regards, Mick

19/01/2014 19:42:07

Hello Mick,

I work in the field of testing and developing prototype engines, both petrol and diesel. These are full size ones though, not model scale!

Exhaust temperatures measured at the header pipe, just after the exhaust port, can reach 900 degrees Celcius for a modern fuel injected petrol engine when at full power. I am not sure how this might relate to a very small cylinder as in a model. The fuel is still the same and if using similar compression ratios then the cylinder pressures and therefore bmep will be similar too. The temperature is not constant of course and so the valves and seats will heat and cool rapidly.

I'll do some further digging on this subject.

Regards,

Mick

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