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Member postings for Robin Dufton

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

Thread: 2 Inch Ransomes
11/07/2021 07:23:36

Ok. I guessed there would have been more interest in this, especially the steel boiler to our design, as we must be doing something wrong. I guess we'll go back to building it behind closed doors.

Thread: advice old British motorcycle
07/07/2021 00:01:54

I've always liked the look of the Sunbeam S7 Deluxe for the American styling although they're over budget. £5k is a bit tight for a decent classic bike as even Noddy bikes are £2k. I have my well used RGV250 up for sale at the moment for £6k, and mint bikes are over £9k, as classic bikes prices are through the roof at the moment.

Thread: 2 Inch Ransomes
06/07/2021 15:26:31

We've been a bit light on progress recently as we've had a fair bit of work to get through. The last of the riveting. 700 rivets in total between the tender and belly tank.

Thread: Milling machines - western-made s/h recommendations up to 2k
04/07/2021 21:03:55

We've used Matt in the past to shift stuff and been very happy.

You say it's 15' x 8' and have ruled out a large knee mill. The manual machine space in our workshop is that size and has two lathes, drill and a Bridgeport type mill. If the small lathe were gone you have bench space and our walkway is free space to put something like a saw. The mill cost considerably less than £2000 and is like new. It came from a company who repaired weaving looms that had shut down, and had spent it's life making small brass parts. Two of us moved it in our Transit van with an engine crane.

Thread: Fowler Build
27/06/2021 21:28:05
Posted by Paul Kemp on 27/06/2021 20:16:48:

Nice to see some common sense on stay spacing there Robin instead of the usual hysteria! As Jason said steel for the 3" for the OP makes far more sense than copper.


There seems to be a lot of pearl clutching when it comes to steel boilers. I've seen it in old model engineering books that a steel boiler should be 1/4" thick with no evidence to back it up other than best guess or rule of thumb. Our boiler could be 0.27mm thick and take it's working pressure, plus 1mm for waisting, so 1.27mm total. 3mm is plenty. The ASME regs, which I found after doing my calcs and sending them to the boiler inspector, backed up my calcs.

The only thing the boiler inspector questioned was using 3mm thick steel for the firebox and he requested 4mm. I'm happy that 3mm would be fine, although it is 4mm as we're not going to argue or upset anyone, especially someone that experienced and helpful.

27/06/2021 15:34:20
Posted by JasonB on 27/06/2021 10:09:56:
The other advantage of going for steel is you can get the pressure up a lot higher which will help with the R3 being a compound.

When I did the calculations for the Ransomes boiler I also worked out the yield stress for Haining's copper design and it was below the 2x test pressure, something like 11bar without looking at my notes, vs 12 or so. The yield stress for my steel design is at 40bar and it would reach it's UTS at 70bar. At working pressure the sides between the stays moves outwards by 5 microns, it could have just about passed a 16bar 2x pressure test with no stays.

We settled on 8bar, even though it could have been run at 15-20bar, as we made the pump to his design so it seemed like a reasonable compromise and it is 30% higher than the copper design anyway. We could have redesigned the pump although we've changed enough of the design already.

Edited By Robin Dufton on 27/06/2021 15:35:58

26/06/2021 20:21:38

Tony Baldwin of AJB has retired and he was also Bell Boilers, as when I rang him the caller id said Bell Boilers. What scale is it?

Rather than worrying about leaks you should really focus on getting started. Things like that can be solved when it's finished. If you're doing it odd evenings and weekends you're a couple of years away from it being finished.

Edited By Robin Dufton on 26/06/2021 20:23:51

18/06/2021 19:46:56
Posted by Roderick Jenkins on 18/06/2021 10:18:43:

It looks like the maximum speed of the mill is 3000rpm which is slightly faster than mine, so definitely worth a try.

I wouldn't bother without a spindle speeder and they do occasionally come up second hand. 3mm is pushing it on a manual mill, trying to cut with a 1mm cutter would be pissing in to the wind, but then people use face mills in little Chinese mill drills.

Thread: Calculating Diameter
12/06/2021 17:08:36

I guess you want to know the minor diameter. If it's metric just subtract the pitch. Pocket Ref

Thread: Best choice of material
11/06/2021 23:46:39

I've never understood this idea that top slides lack rigidity. There will be a screw to lock it against the gib strip. Take it out and replace it with a handle.

Thread: Cyclemaster engine rubber bushings
09/06/2021 21:42:02
Posted by J Hancock on 06/06/2021 13:45:50:

If you visit a decent electrical distributor , you should be able to buy a two-pack self-setting hard rubber compound that would do that job perfectly.

Potting compound wouldn't be ideal as it's often a hard setting epoxy.

We use this stuff for reproducing NLA rubber parts on vintage bikes, just pick a suitable hardness and make a mould. Give it a few days to cure and you're good to go. Link

One piece of advice with castable PU. To reduce the chance of getting bubbles when you mix the two parts, put the bottles in warm water before pouring it out.

Edited By Robin Dufton on 09/06/2021 21:44:01

Thread: Dividing head - Beval gear ?
08/06/2021 21:52:11

I remember reading something like the worms on small dividing heads and rotary tables are peened in the factory to reduce backlash, as they're too small to fit in any other way of eliminating it. Even with a new worm gear it may be more hassle than it's worth getting it set up correctly because of that.

If it's a well made unit from a decent company that has a few parts missing, and worth saving, there is the option of buying a foreign copy and stripping it for parts.

Edited By Robin Dufton on 08/06/2021 21:52:26

Thread: 2 Inch Ransomes
07/06/2021 16:15:32

More progress. Finished the rear wheels and crankshaft, just some tidying up to do on the counterweights from being laser cut. We also managed to work out a system for building the wheels and them ending up straight, unfortunately we only worked it out on the last one, so if the others don't look so brilliant when it's running we may redo them although they're all within 0.25mm in all directions.






Edited By Robin Dufton on 07/06/2021 16:19:18

Edited By Robin Dufton on 07/06/2021 16:19:37

27/05/2021 17:29:34

I can't see 4 inch steel tube in anything other than 1/2" wall thickness on there.

27/05/2021 16:13:19
Posted by br on 27/05/2021 16:03:40:

Bought my last lot of 4 inch from Joe at maccmodels . I see he has it in stock

Has always been helpful and will cut to non listed lengths


Didn't think to ask one of the model suppliers. The fire tube material is coming from them so we should have asked about tube, although the only stuff I can see on there is 1/2" thick.

27/05/2021 15:24:42

Finally got all the bits together for the boiler. Getting 4 inch tube was an absolute nightmare.

Thread: Thread on front forks on a Raleigh bike
24/05/2021 16:04:58
Posted by Bo'sun on 24/05/2021 15:35:48:

The headset is going to have to change anyway, along with the stem, if Mike decides to go down the threadless steerer route.

Many combos of modern parts aren't guaranteed to work on old Raleighs. I had a headache when trying to sort out a 70s bike and had to make a bush for BMX bars to fit. No stems would fit the fork so it had to be the Raleigh specific stem. Changing the forks would have meant making new bearing cups.

Thread: 2 Inch Ransomes
23/05/2021 21:00:41

So many rivets. So many rivets.

12/05/2021 16:33:53

We got started on the smoke box. I should have taken some pictures of the flat plates before rolling.

Edited By Robin Dufton on 12/05/2021 16:47:18

Thread: Can one buy pliers with parallel jaws that lock like mol
05/05/2021 19:12:59
Posted by bernard towers on 05/05/2021 18:34:47:

Why not drill the handles of photo 1 and fit a threaded bar arrangement or a cam?

That would be an expensive and elaborate toolmakers clamp. We have some of these hanging around for clamping sheets and blocks together for marking out and drilling.

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