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Burrell Single Crank Compound Traction Engines - 4" Scale

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steamer:
That's beautiful work Andrew!   I l really like that pump! :ThumbsUp:

Dave

jadge:
Dave: Thanks for the compliment. I had quite a lot of help over on TractionTalk from somebody who designed pumps commercially. He mentioned a whole load of parameters I hadn't thought of and challenged me to show that the pump wouldn't cavitate on the suction stroke. It took a while but I managed enough theory to convince myself that it wouldn't cavitate. He also suggested glass filled PTFE for the wing valves rather than the bronze I was intending to use. I will be interested to see how the glass filled PTFE behaves when being machined, as pure PTFE is a bit of a pig when trying to hold exact sizes.

Peter: As promised here is an outline of making the taps. The taps are made from silver steel (aka drill rod). Cutting the basic threads, turning the shank and forming the drive square are all straightforward. The taps are serial, ie, taps 1 and 2 do not cut to the full depth. I took values of 41%, 81% and 100% of full depth for each tap from Machinery's Handbook.

For cutting the flutes I used 1/8" radius cutter  on the horizontal mill, the depth of cut being determined from a CAD sketch, adjusted until it looked about right. Note the home made extension to the dividing head tailstock to avoid cutting into same:



The taps were hardened in the electric furnace, quenched in brine and then tempered at 215C. I ground a relief on the tapered portion of the taps as it gave me an opportunity to try out the drill and tap grinding accessory I bought last year, although it would have been just as easy to use a needle file before hardening:



I made the two nuts as one to start with, to ease holding. In this picture the threads have been counterbored with a " slot drill to shroud the sharp edges where the thread starts:



I made a couple of boo-boos when making the taps. First, I failed to notice that the size of the small end of the taps should vary as well as the depth of thread. If I'd done that the taps might have required less effort when cutting the thread. Second, I failed to harden the first tap properly, so it twisted slightly when being used.

Nevertheless it was an interesting exercise, and it's another tick in the been there tried that boxes.

Andrew

Jo:

--- Quote from: jadge on May 31, 2015, 10:24:32 PM ---Dave: Any resemblance to a kitchen is purely accidental. It is actually the assembly hall, casting storage area, and potential workshop - spot the coil winder, dead weight pressure tester and Pultra lathe on the table. I just happen to cook in the same area.
--- End quote ---

:lolb: Sounds like my dining room table.. I just happen to eat off it.

Jo

pgp001:
I bet your kitchen assembly hall floorboards are groaning a bit  ;D

Phil

peatoluser:
Andrew,
thanks for the photos/explanation of tap making. specially the depth ratios. filed away for future use

peter

(apologies, for some reason I called you Dave! - (i blame the beer!)
post properly amended

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