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General control line discussion => Open Forum => Topic started by: Motorman on October 19, 2014, 10:27:04 PM
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What alloy steel is used, is it heat treated, drop forged, cut/grind from bar stock? Talking about a modern high performance engine like a Rossi, Picco or OS Max.
Thanks,
MM
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These are just guesses, but:
That's a secret,
probably,
probably not,
probably.
And, of course, it varies from manufacturer to manufacturer.
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There is a drawing here with material nad heat treatment info:-
http://www.machineconcepts.co.uk/aeromodelling/brians_engine/shaft.PDF (http://www.machineconcepts.co.uk/aeromodelling/brians_engine/shaft.PDF)
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I'm retired metallurgist.
Grade EN24 is European version of a high quality, high tensile,nickel chromium molybdenum alloy * (1.5% Ni,Cr,Mo) steel. US equivalent to SAE 4340. I'm sure there is a JIS version used in Japan.
Typically sold T’ ( soft/ tempered )condition, to facilitate machining operations. Then given the final heat treat
too provide combination of high tensile strength, shock resistance, good ductility and wear resistance.
For crankshaft in model engine likely begin with round bar stock. Too expensive to forge or to apply special treatments such as carburizing or nitriding.
*Chemical Composition %
- Carbon 0.35-0.45/
Silicon 0.10-0.35/
Manganese 0.45-0.70/
Nickel 1.30-1.80 /
Chromium 0.90-1.40/
Moly 0.20-0.35/
Sulphur 0.050 (max)/
Phosphorous 0.050(max).
*
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so ..... who is going to make me a lefthand crank for a PA75 ?
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so ..... who is going to make me a lefthand crank for a PA75 ?
You can do it with a Saito 56/62/72 by just buying and replacing the cam gear ;D
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I have worked on large crankshafts used in 12 & 16 cylinder diesel locomotive engines. They start life as a large forging.
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This link has all you want to know about crankshaft forging.
http://www.ellwoodgroup.com/Education/Crankshaft-Forging.aspx
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Thank you Lyle that's what I was looking for. Any idea where I can get some 4340 in 3/4" dia?
MM
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Thank you Lyle that's what I was looking for. Any idea where I can get some 4340 in 3/4" dia?
McMaster-Carr ($$$), Metal Supermarket, Enco (enco-usa.com, I think).
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http://www.onlinemetals.com/merchant.cfm?pid=7388&step=4
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I was about to suggest same sources as above. Another is Advanced Global Materials. Direct Phone: 631-286-8570
I think they are on Long Island. They have web site and you can request quote online.
Many other steel distributors out there who cater to aerospace & energy industries.
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We had the crank break in a McCoy .50 once years ago...the prop/spinner and all flew off. We had a buddy that was a machinist make a new one. It looked just like factory, and we ran it a couple times after that, but can't remember much about how hard it had to be. It could be that it was hardened after he made it. H^^
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MM;
http://www.ebay.com/itm/3-4-Dia-x-24-Long-4340-Hot-Rolled-Annealed-Round-Bar-3-4-Dia-4340-Annealed-/200668570736?pt=LH_DefaultDomain_0&hash=item2eb8c76470
r/
Dave
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What do you think of 4140? I just remembered I actually have a piece of that given to me by Al Stagens who used it to make cranks for his super modified Cox TD.
MM
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My steel of choise would be ball bearing steel 100Cr6. It's quite easy to machine in soft state and has nearly perfect properties when properly heat treated. It is a total metallurgical overkill in our little engine.
I have no idea how complicated the hardening process is as we outsource it to a ball bearing factory.
L
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so ..... who is going to make me a lefthand crank for a PA75 ?
You don't want that. Even the electric guys are going back to conventional rotation.
Brett
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You don't want that. Even the electric guys are going back to conventional rotation.
Brett
This needs more explaining, the only down side I have seen is the difficulty in finding props. Other than that I like everything about flying a reverse rotating engine.
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You don't want that. Even the electric guys are going back to conventional rotation.
Brett
Huh? Could you explain who "the electric guys" are? Maybe you could get them to explain why? I'm just curious as to your statement. I'm sure there is a lot behind it.
Thanks.
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Huh? Could you explain who "the electric guys" are? Maybe you could get them to explain why? I'm just curious as to your statement. I'm sure there is a lot behind it.
Thanks.
Difficult to have good takeoffs, difficulty trimming in the hourglass, a host of issues.
Brett
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I use our MB engine with pusher props but only because of some anomalies in engine run that I have not been able to fix yet. At the moment it's better like that, but as soon as I get the running fully symmetric, I'll go back to normal rotation. Getting props is no problem as we cnc them by ourself. L
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4130 to 4340 steel, HT to 160/180 KSI, maybe 200KSI, (this is how Boeing generally calls out HT specs...tensile strength in thousands of pounds per square inch) would be my choice. Strong stuff at that HT, not brittle yet, and nice to machine as long as you are using carbide cutters. In soft condition, it's very gummy and the finish is horrible...smears/tears. All those are very abrasive to cutters, due to the chrome and carbon.
By the way, it is entirely possible to get a piece of the above that meets the specs for both alloys, because of overlap in the tolerances. Also, there sometimes are alternate materials that are ok'd to use for a part, so don't get too myopic. H^^ Steve
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The last crankshaft I machined for a small diesel I was building, I used a grade 8 bolt of sufficient size so that the whole crank including the crank pin could be made in one piece. The head of the bolt provided the material for the crank disc and the crank pin. The crank machined and finished well, and works like a charm... the material was easily sourced at the local bolt supply house.
Orv.
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I would like to have a reverse crank shaft for an OS LA.25 if some one gets to doing this kind of work. I want to put it with a stock OS.25 in a Sheeks Mosquito stunt model. There are some props available that I can get in the sizes needed in both right and left hand versions, and can repitch as necessary. I just think this would make a cool model! Lots of interesting things to try with this example. The inspiration was Walt Brownell's twin electric stunt model that was about the same size, and I think he even inspired Bob Hunt with that one at the same time. Anyone that can whip me up one for a reasonable price, send me a quote!
Type at you later,
Dan McEntee
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My heat treating oven only goes to 450F so it's only good for drawing temper. These chrome steels need to go to 1500F then cool to 1200 then 850. I could get it that hot in my charcoal foundry but I can't control the temp. Things like crank webs and intake windows get warped anyway with heat like that and I don't have a shaft grinder. I was hoping for something I could machine then use without heat treating.
MM
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Getting the material is easy enough. Order the material already heat treated to 160-180 KSI and machine it. Or use a grade 8 or grade 10 bolt, like GG said. Look up the specs on the bolts and see which you want. No heat treating required with either method. What engine are you wanting to make a crank for? Picco .8cc? D>K Steve
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To use without heat treating I would use ETD 150. That has a minimum 150,000 PSI ultimate with 130,000 PSI yield. Strong, tough and no post machining required. If I wanted something stronger, I would go with 17-4 or 17-7 PH Stainless. You can age 17-4 or 17-7 PH Stainless by putting it through a self cleaning cycle in an oven, but it would most likely need need to be finished after heat treatment. It can be machined with a ceramic coated insert in the aged condition.
Pat
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For quality heat treating of steel I suggest contacting a company known as Bodycoate. You can find them on a google search and ask them. They have shops where they provide HT services . Not sure what they would charge you for a small piece-perhaps they can run it through together with one of their commercial jobs. You never know unless you call and inquire. Should be very routine for them.
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This needs more explaining, the only down side I have seen is the difficulty in finding props. Other than that I like everything about flying a reverse rotating engine.
Maybe it would be easier to learn to fly clockwise than mess with the cranks & props. Some winneer did it in the past.
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Or use a grade 8 or grade 10 bolt, like GG said.
Bolts are made to bolt, not to be machined easily. Moreover, there's no requirement on the bolt manufacturer to use any one material or another -- just to get an end result.
So getting a bolt and machining it will be luck of the draw -- ordering steel of your desired alloy at your desired temper will be much more controlled.
Steve is used to using nice rigid machines, so he fails to mention that not only do you need carbide steel cutters to machine the stuff he's talking about, you also need good equipment. If you've got a cheap Chinese lathe, machine flexibility may prove to be an extra challenge.
I suggest that if this is your first crank, than you just make the thing out of plain leaded steel. It'll be ridiculously easy to machine, and the only issue with it not being tempered is that it may wear faster. Then, when you know how to machine cranks, start using more challenging material.
(Oh -- and consider getting a tool post grinder. Yes, you have to be careful of grit in your ways, but you'll have a way of grinding shafts.)
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I beg to differ with Tim,
Fasteners, particularly high-strength ones are manufactured and heat treated to high industry standards. Grade 8 bolts are medium carbon alloy steel and heat treated to a hardness of between 33 and 39 Rockwell C.
The high strength bolts machine very well. A case in point, I machined a complete crankshaft for a small diesel engine I was building from a Grade 8 bolt.
To test my skill and daring, I machined the whole engine along with the crank using my "toy" lathe... a Unimat SL1000. I used a high-speed steel cutter bit. Because of the small lathe's limitations, I had to do a large number of cuts and I don't think I sharpened the tool until I did the final cuts. I will use this material again on my next engine but I will not use the Unimat!
The attached photos show the engine and the tools I used.
Tim is right in that grade 2 mild steel bolts, along with cold-rolled steel, machines to a poor surface finish.
Orv.
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Nice work, GG, Unimat or not! What is the function of that pipe & casting doodad behind the lathe?
Say "Hello" to Monty for me! H^^ Steve
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Orv: I'm not saying that you can't be successful with a grade 8 bolt from the hardware store (I've used them myself for various machined parts). I'm just saying that if you depend on them for their machineability you may be disappointed one day.
And it's a cool engine -- the best I've managed so far is to replace all the moving parts in a Cox TD 09, which wore out about the same time it got broken in.
Steve, that's a milling machine adapter -- you unplug the head from the base, plug in the milling adapter, and tra-la, your flexible lathe is turned into a flexible-er milling machine. (I've got one of those lathes stuck off in a corner someplace).
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Thanks for the kind words Steve.
That doo-dad is a vertical column structure that allows one to convert the lathe into a drill press and milling machine. You replace the headstock with the column and attach the headstock to the casting on the column. The headstock incorporates a lever actuated spindle much like in a regular drill press. This is a pretty versitile machine in that you can turn tapers and drill angled holes etc. The tricky part is setting the Z axis when you are using it as a mill since there is no fine feed. I make precision Z axis feeds using my caliper to measure the distance between the back of the spindle and the headstock casting. This takes three hands!
I also used this machine to make all of the special fixtures and tools like hones and laps for the piston/cylinder fit.
I could have built this engine in about 1/10th the time had I used my good machine shop tools, but I was challenged by a friend who said it wasn't possible.
Monty is well and we have been out a number of times flying together. I will pass on your greeting.
Orv.