Member postings for Martin Johnson 1

I think the LMS steam turbine loco had a similar arrangement to isolate the reduction box from the drive axle.

There is a diagram here

**LINK**

See 8th diagram/picture.

Martin

I had forgotten Tuby's blue Burrell. There is also Renown and Repulse in blue for the Fowler camp and Lightning Ii in green for Burrell.

So within reason, do it the colour you want. I think the mustard menace illustrated above is the height of bad taste.

Martin

I would guess they are cast iron, so it really should not be an issue to reduce the excess to swarf in fairly short order. Carbide tool, generous feed rate, modest speed, coolant to keep the dust down. Go for it.

Martin

I bought Qcad for about 30GBP 3 years ago. Generally very good as a 2D package and is also available at no extra cost in 32 or 64 bit, Windows and Linux options.

Changeover from Turbocad was pretty minimal.

Qcad at 30 quid seemed a more reliable option than free Librecad to me.

Martin

I would go with Viton as it has a higher temperature tating and better oil resistance than nitrile (or Buna N). In addition to perceived engine temperature you have higher temperature at the piston head plus local friction at the O ring to allow for.

Martin

Whether you go for solid or soldered, they will be easier to handle as a strip of 6 plus sawing allowance plus a spare or two.

I would go for solid.  Set raw stock up in rotary table (spindle horizontal) two endmill passes to get the flat feature, then several passes with table rotated to form the round feature.

Martin

Edited By Martin Johnson 1 on 01/05/2023 12:51:41

I have a lathe with L00 fitting. Easy way to change chucks is to hook the C spanner to screw into the headstock. Get a suitable bar to sit between chuck jaws then heave one against t'other.

I like the fitting as it is very quick to change chucks which is useful to a model engineer.

Martin

I managed run of the mill model engineering for many years using a Lidl £10 special.

However, I had to ugrade to Mitutoyo when machining a large and expensive crankcase casting for rolling element bearing seats (so tight tolerances).

It all rather depends on skill and feel plus the job in hand. Many people could not make use of the better sensitivity of an up market tool. I play piano, but a Steinway grand would be wasted on me.

Martin

As SOD points out, if the clearance angle is greater than the nominal 5 deg then it will still cut.

For boring, above centre height reduces apparent top rake, so a little can help get the tool down the hole, but dont overdo it.

My own view is that tools should be set to centre height to +0/-0.25mm tolerance.

Martin

The DO that I ran had a very poor drawing stoore, cold and a bit damp. Storage was in conventional wooden flat plan chests. We had linen around 50 years old and very little degradation other than wear and tear was evident. We routinely printed drawings using the ammonia process with no harm. I think water is the one thing to avoid.

Martin

I think Vince Gingery did a book on making a DIY version of the Gabro. Have a look at Camden's book list.

Martin

Trevor beat me to it. They have a grease or oil reserve and slow reacting chemicals that force rhe lube out over a period.

Martin

Nigel,

It would help to know what you building.

I designed and built Ackerman steering for my 7" scale lorry using "Elements of motor vehicle design, second edition by Donkin. As pointed out, you will probably need quite low gearing as you will be way over scale weight on the axle. That being so, forget about self centering steering. You will need more than 3 turns lock to lock. Full size HGVs back then would have 4 to 5 turns.

I dont agree with some of the comments about setting the Ackerman arm angles, track rod length etc either.

Pm me if you would like a part scan of Donkin. It might even be on t'internet.

Martin

I agree that needing a blind, rectangular hole with sharp corners is very poor design. And yes machine shop foremen can eat a rookie draffie in a single mouthful. There has to be an alternative.

dc31k - you could have politely pointed out that rotary broaches can not do rectangles. It would have had more impact.

Welding/bolting/glueing a piece with a through rectangular hole onto or into the larger piece would be my favoured option.

Martin

Some people would view it as an instrument of torture, watch "Saturday night and Sunday morning" if you dont believe me. I can remember that by early afternoon the coolant fug over the capstan shop was so thick you couldn't see the far end.

Despite that a really useful and versatile tool. In later years many spares orders for 1 off were turned out on capstans - easier to set a capstan than disrupt a run on CNC lathes.

Enjoy, but not by chasing production bonus.

Martin

The price for the 12mm mill drill certainly caused a sharp intake of breath here. I think most model engineers must have a bigger edge tool budget than me.

Martin

When you have the lathe set up to cut a morse taper, run off a few bits of dowel to make cleaning tools. Glue on some chammy leather for a deluxe version. It really isn't difficult if you think ahead.

Martin

Thanks for the clarification James. There is certainly more to these simple little engines than meets the eye.

Martin

Noel,

I think you are doubting my numbers on coal consumption. Happy to share my spreadsheet of IMLEC results. Pm me and we can exchange e mails.

Jasonb & Hopper,

If starting from zip, then I think you are probably right. Usually needs some refractory at the end of the furnace tubes as well. I had conversions or trying to keep a full size outline in mind.

Philip Gardiner,

Good point that draught will almost certainly increase, so more mods needed to blast pipe & chimney. Turbulators might well work, but I think they increase path length rather than Reynolds number. I can also see that an arch increases flame length and improves combustion.

I think we all agree it is quite a problem to get the best out of gas.

Martin

Interesting addition - Dockstader treatment for oscillators! Well done.

I am intrigued by the compression loop and even more intrigued by the expansion loop. So what is going on there?

I suspect managing those loops could be key to getting good running.

Martin