Is it possible to make a scaled down version 350 chevy crank on a smithy 1220xl?

Modat22 wrote in news: snipped-for-privacy@4ax.com:

You will need at least a 4 jaw independent chuck, and some method of offsetting your tailstock by the amount of the crank throw.

Hmmm.. I would just make up a pair of plates, with the cluster of crank centres drilled and countersunk, then fasten the crank blank to that, and turn each between centres.

Take care.

Brian Lawson, Bothwell, Ontario.

Why don't you talk to the Bay Area Model Machinists (BAMM) They were all over the model machining show in Visalia a few weeks back. They got bored with naturally aspirated Chev's and are now build Rootes type blowers for their 12 c.i. models. Leigh at MarMachine

Nope! Offsetting the tailstock yields a taper. The tailstock must stay in dead alignment with the spindle. It is the crank that must be offset. What one generally does is make a large diameter cylinder at each end that has matched sets of center holes so each of the throws and the mains can be turned using the proper set of centers. There's a few ways to accomplish the task and have the centers in proper relation to one another, but a mill should be used, not a drill press.

It might be a good idea to make a couple simple cranks and get the feel before jumping in on a crank for an 8 cylinder engine, even a V engine. Lots of room for error, and way too much work to risk scrapping, which is sure to happen if you're not familiar with making cranks. One of the things you will face is the material moving about as you machine it. It's more than a good idea to rough everything and go back for finish cuts.

Good luck!

Harold

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"Harold & Susan Vordos" wrote in news:419045c3$1 snipped-for-privacy@newspeer2.tds.net:

Well...that's what I was trying to say....but didn't make it very clear..... The throw you are machining must be on center, but the snout and flange of the crank will not be.

Hey thanks for the reply. I knew I'd have to offset the crank somehow. Should do a rough balance before I start machining to protect my lathe bearings? Or is the speed going to be so slow that lathe damage shouldn't be a problem.

Still, how do you turn a crankshaft? I understand the part about offsetting one end in a four jaw chuck, but how do you tailstock the other end to remain stable while maintaining the desired axis of rotation?

Harry C.

The best answer to this is to find some books on modelmaking. They will explain it much better than we can and have pictures. Some of the best advice I have received here is to read a certain book. There are numberous books on making single cylinder cranks. Perhaps Ron addresses multi-cylinder cranks in his book on building the Offy.

After reading the books and looking at the pictures, you will be able to decided if you are up to the task. Another very educational thing is to go to a good model show. Cabin fever is coming up in Jan. There you will be able to see challenger V8s, Offy and even some small block chevy V8 castings (guy won't sell em though). You will even get to hear them RUN!

chuck

Bearings shouldn't be a problem, but counter-balancing is a great idea, if for no other reason, you'll be able to run faster than you otherwise could. Even if you don't need the speed for turning, it will be handy for polishing after machining. As the turns become round, you would likely prefer a higher speed than would otherwise be advisable, too. Bear in mind that the material is constantly changing in mass, so the best you can hope for is a general balancing. Naturally, it will run differently when doing throws as opposed to doing mains, which should be in balance if all throws have been turned.

Be very mindful about roughing, as I said earlier, and don't overload the center. As you machine away the throws, the crank will become quite flimsy. You'll have to take special care to prevent chatter and springing from tailstock pressure. It's sort of a juggling act.

If you can find a way to index the crank, it can also be machined from soft jaws in an offset bushing. All throws can be machined from the end main that way. It helps shorten the crank while machining, but presents its own problems, too.

Good luck!

Harold

I should be able to answer this question, but.. It's been a long time.

You need like a four way chuck on each end with centers and a way to index what ever a V8 is (maybe off the dogs). The one journal crank is the hardest to re-grind. The crank is off set to its stroke and indicated off of the mains (mains are ground first and now off set like the rods usually are) and worrying about taper in the machine. Also each end should be counter balanced. It takes some time to set that up even with the right machine. Building the first crank should be easy compared to setting up after the fact. Off hand I can't recall the set up to get the 2 axis/4way chucks lined up , I'd have to stand in front of a crank grinder to remember. It helps to think 3D and in motion and realize what is driving what while holding it solidly.

Go to

scroll down to "special engine articles" click and scroll down to Scorpion V8. Buy those back issues and you will have everything you need to build a model V8 engine. Other articles cover just about any type of engine you could want. If you are serious about building model engines, Strictly IC is the mother lode of info. There is no other comparable source in the US and maybe the world.

Randy

--Is this a different group than BAEM? Got any contacts??

Hey thanks this is the sort of information I've been beating around for. As I look at this site I can easily see myself spending a couple hundred dollars just on back issues LOL

I will second this advice. Strictly IC is the premier source of information for model IC engine builders.

One warning, however. Once you buy one year of SIC, you will want to buy all the rest. This is convenient, however, when your spouse or relatives want to know what to get you for Christmas. Just give them the SIC list, marked with the years you already have. :-)

SIC also has lots of general machining articles, such as making hobs for cutting gears. I wish it were still being published, but Bob Washburn has done the next best thing by keeping all the issues in print.

Alan

snipped-for-privacy@yahoo.com (Harry Conover) wrote in news: snipped-for-privacy@posting.google.com:

For a small crank such as the OP stated, I would probably machine a flat plate with a hole/bushing offset to the proper throw, with a taper clamp or set screws, and a center drilled on center. You could place the bushing on the snout, set the taper lock/set screws, and it should be rigid enough to chuck the center in. If you are worried about spring, leave extra material on the counterweight/throw next to the snout and make a stabilization spacer to go between the plate and that throw.

Of course, the easiest way to rough it out, is like the big guys do, with a milling machine and about a 4' dia cutter. The crank remains on center, the rotation/offset is interpolated around the throws.....very interesting to watch. The only turning occurs on the very first operation, they turn the snout, and flange, then to the mills then drills and then they go straight to the grinders, then polishers from there.

Book: The Shop Wisdom of Philip Duclos from Village press, publishers of Home Shop Machinist magazine.

Comment: If you have to ask, it may well be that you do not have enough of a grasp on how this is done, to really understand the answers being given in the thread. My suggestion would be to build something (or several somethings) that were a little less complicated than that V8. In particular, the book mentioned above shows detailed set-ups for a single throw crank that shows at least the concept of tuning around multiple centers.

Other good resources: Google for "Strictly I.C." It was a periodical, since discontinued, that was completely about internal combustion engines. While they are no longer publishing new material, ALL back issues are available.

There is also a start-up of a new magazine you might consider subscribing to, info at

. One of the projects they are covering in some detail, is a scale small block Chev engine.

Good luck!

Cheers Trevor Jones