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Discussion Starter · #1 ·
Guys,
I'm not a trained metal worker; for years I stuck to plastic kit bashing. Then I started cutting bits of brass to e.g. make reinforcement for the plastic stuff - especially in this big scale. Now I'm getting out of my depth with large scale work, trying to make things like a complete chassis.

I can (usually) cut a piece of brass in the right place, but I'm at a loss as to how to bend accurately.



This is a square (!) box designed the support an axle, as you can see below, and to pivot so it provides equalisation. It isn't square, as you can see.

What do you use to make something like this? What's the 'proper' technique, or the proper tool? How do you get the sides to be exactly the same length when you bend it?


 

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Pete,
Keep in mind that when bending metal it "stretches". When laying out formed metal parts you need to make a bend allowance for each bend. There are some very complicated formuals for this but when I was working at a sheet metal shop we had a chart that was pretty close. Not "swiss watch" close but pretty good for what we built.

Now we also had neat sheet metal "brakes" that would form up repeatable sizes using "stops" that could be manually set or computer controlled. Obviously we do not have this luxury at home unless we make investments in tooling. There are home sheet metal brakes from a foot long bed to 3 feet long available from Micromark and other sources. These will ahve manually set stops but are adequate for our purposes. I do not yet own one but will someday. In the meantime trial and error (lots of error) can be your guide. I'd use a bench vise on something like what you are doing. I'd also only fold up three sides or almost 4 sides. Leave an opening in the 4th side and solder or bolt the 4 side on. Always leave a way to adjust or hide excess material was the way we managed to overcome inconsistencies in the material. Good luck!

Chas
 

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Pete, sheetmetal work is a trade unto itself, becoming an art at times. Specialized tools and equipment, different than most of us have in our home shops.
Working without this good stuff for your piece, I would start with a hardwood form block to the inside dimensions. Clamp the first leg close to the bend and tap the stock around the corner with a hard plastic hammer, or a piece of wood and regular hammer, to avoid marring the stock.this will give you a fairly tight bend. Remove piece from block and "overbend" a bit by hand to get true 90 degrees. Repeat. I have a small finger brake, but after the second bend, the stock interferes with the shoe, so a form block is the way to go.
Another trick, and you may have done this, is to machine holes, slots, etc, after the bending is done. This way, if the bending is not to your satisfaction, less effort has been lost. Also, machining after allows you to compensate for any bending irregularities.
On the live steam forum have been threads by "redbeard" on building a Forney and more recently, a steam railtruck. Larry does his beautiful stuff with a minimal shop. But, he does cheat--he is a manufacturing jeweler by trade.. Seeing what he does, with many explanations of how it was done, makes for enjoyable reading. If you wished information on how some part was formed, I'm sure he would be glad to explain.

Larry
 

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I'm not a metal worker of course but previous experience in O scale many years ago leads me to believe the "solid" piece as suggested by Dwight is a good way to go. Lobaugh for years made excellent kits using cast bronze frames and besides being accurate they gave good weight down low and lasted "forever".

As an alternative for myself not being too swift on this sort of thing I would use jigs to build up the brass segments. For example using blocks of wood cut to fit inside the squares you made. The brass could then be fitted around the block in four separate pieces, soldered together, corners ground smooth, drilled and bored out and then the wood removed from inside.
 

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Pete,

I've done a good bit of sheetmetal work, usually aluminum. If you want anything like precision, you just about need a brake. Harbor freight sells a short one for ~$80. I have one and it is suitable for anything I've wanted to do. Point of fact, I bought it specifically to to LS work with.

A word on 'radiuses' (radii): Any metal needs to stretch as it bends. Else it'll crack. Okay, one of the 'arts' is to figure out how much 'offset' you have to leave. There are lookup tables, like someone said, but for rule-of-thumb work, offset the thickness of your material. The thicker the material, or more brittle, the more offset you want to leave. How do you calculate that? Experience. Take, say a piece of thin stock. Say 1/32" thick. Scribe where you want to bend, then 'mark back' in the direction of your final bend, that much and scribe a line. Line up the fixed edge of your break with the second mark, clamp and bend. You'll come out fine in most cases.

Always use one end or the other of your break, because these cheap ones tend to flex in the middle ever so slightly. Especially with heavier stock. Besides that, you can use the end mechanism to keep the material from 'crawling' as you bend it. Try to do your bend in one, controlled movement. You don't have to be fast, just steady. Slow and steady works real well for me. I use a pair of 'deep throat' visegrips on top of a 3/16"(?) piece of steel flat stock for a top clamp. An old 6" planer blade is good. And a 4" for narrower pieces. Mine's about 1" wide. You don't want it too wide or it'll get in the way.

Don't be fooled by Micro Mark's 'Vise Finger Break'. No bench vise is machined so that it won't have slop. And they'll want to twist as you tighten down.

One last word: the thicker the material, the wider the radius of the bend. You have to do that unless you've got precision tooling and special metal to work with. So on very thick material, like 1/8" (and that's crowding it for brass unless it's annealed) and up, strike your 'deadline' and offset line, bend a little while watching for the workpiece to see it doesn't start to twist 'n crawl; offset again and bend again, and so on until you hit just past 90 deg. Then measure all the way around the bend and you'll know how much material it actually took, and you can figure the location of your next bendline more accurately.

You can try annealing your brass, first. Off the top of my head, I don't see why that wouldn't work but I've never done it. Another dodge you can think about is to try using soft copper for the frame with machined brass bearings. I'm not saying that'll work, but it will allow you to bend up a 'box' a lot easier. Or see if you can turn up some 6061-T6 aluminum. That stuff is the very berries to work, though if you crowd the corner too hard, it'll crack too.

Hope this helps.

Les
 

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Discussion Starter · #9 ·
Gentlemen,
[The term of address has been upgraded, as you've all been so helpful.]

Many thanks - you gave me the feedback I ws looking for. You collectively pointed out that what I was doing wasn't that easy, so I'm not totally off the wall in being concerned that I was doing it wrong! Lots of good ideas and suggestions - again, many thanks to all.

And you reminded me that a jig (or a hardwood form,) is the way to get repeatable bends and to keep the piece in the right place while you make it. Duh!

While a solid block might be the way to go if you have a machine shop that can millout the center, my condo doesn't even have room to put my vertical dril on a bench - it is still on the floor! I did drill the holes afterwards, so at least they were square at one point.

Jason's suggestion of starting with something nearer the shape you want, such as a brass channel, is also good. This piece is 1" wide with 1/2" sides, and I didn't have a source of square brass channel that size - but I'm sure I could have found something. Maybe a 1" square tube would have worked - or I could have made it from a slice of a circular tube: ~1" brass tube is readily available at the plumber's supply? Hmmm.... yes, I like that idea.
FYI. Here's the project so far. That equalisation piece can just be seen on the RH axle.

 

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There is an easier alternative for the part that you are fabricating. Rather than trying to bend a box section over a form or in a press brake, why not purchase square tubing in the material that you want to use. Square tubing in a large variety of sizes is available. You may have to look for a suppply source other than hobby and model shops but square tube is available. The only issue for you then is drilling small holes for the guide and milling the round end slot that sits in the bearing race on the axle. You will need to support the stock with a backer to perform the drilling operation so that the tubing does not deform from the drill force applied. The same is true for milling the round bottom slot.

An additional suggestion relating to the choice of material. The box is brass and the bearing race is brace. Brass and copper in bearing circumstances are rarely paired because when either copper or brass rubs on copper or brass galling occurs and eventually the shaft will sieze to the support. It might be better if you used steel for the square section axle support that you are fabricating. Even high quality lubricants will not prevent galling they will just delay the inevitable seizure.
 

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Thanks for pointing out a source of misunderstanding. I agree that brass bearings rotating in copper frames won't last. What I had in mind was the bearings would be fixed in place (i.e. either rectangular on the outer dimensions and set in a slot, or they would be soldered, staked, pressed or fixed so there was no brass/copper rotational contact.

Good catch.

Les
 

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Discussion Starter · #13 ·
Will all the axles save the driven one float?

Les,

This was a B'mann big hauler / ten-wheeler, so the blind drivers are smaller than the flanged ones. They'll have to be off the rails or they will wear faster than the flanged ones. I am using the orginal bottom plate to keep the axles from falling out, and I have put small pieces of square tube under the bearings so the can't drop too far and touch the rails.
On the other hand, if the front axle is to pivot, then the nearest blind driver will probably contact the rail when the corresponding front wheel tilts upwards on a piece of not-level track. So I ground its slot higher in the frame, allowing it to lift slightly if it contacts the rail. Gravity, plus the wiper for the chuff, which is sprung onto the drum on that axle, should persuade it to sit down most of the time. Hopefully.

An additional suggestion relating to the choice of material. The box is brass and the bearing race is brace. Brass and copper in bearing circumstances are rarely paired


NYC Buff (no real name?) Point taken, but the bearings are not allowed to rotate in the chassis or equalisation frame. (I put some rod underneath to hold the wheel assembly in the frame - it is tight against the bearings and can be soldered if they show any sign of trying to spin.) The axle is steel (I hope) so it is the same arrangement in the original engine.
 

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Posted By Pete Thornton on 11/02/2008 1:28 PM

Will all the axles save the driven one float?

Les,

This was a B'mann big hauler / ten-wheeler, so the blind drivers are smaller than the flanged ones. They'll have to be off the rails or they will wear faster than the flanged ones.


/// Pete: Now there's a remarkable piece of information. Why would the blind drivers be smaller? To reduce wear? But if all wheels are carrying the same amount of weight--roughly--why would the blind ones wear faster? I'm going to have to look into this because I have some half-cooked plans to 'float' all the drivers but one (the driven one) on a B'mann re-bash.

On the other hand, if the front axle is to pivot, then the nearest blind driver will probably contact the rail when the corresponding front wheel tilts upwards on a piece of not-level track. So I ground its slot higher in the frame, allowing it to lift slightly if it contacts the rail. Gravity, plus the wiper for the chuff, which is sprung onto the drum on that axle, should persuade it to sit down most of the time. Hopefully.

/// Yes, I'd think that'd do it.


Les
 

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Discussion Starter · #15 ·
Why would the blind drivers be smaller?

Les,

You're overthinking it - the simple answer is that Bachmann didn't want the blind drivers to touch the rails. (And they are not alone.) On R1 curves (2' radius) like the plastic ones in the train set box, the center wheels aren't even over a rail!
 

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Pete,

Thanks for the info: I now know what the radius of the plastic track is. I hadn't realized the B'mann's middle drivers weren't touching the rail--not got a chance yet to sit and actually mess with the stuff. There's a prototypical fix for that used by at least one logging outfit out west, and that's to lay rail to compensate on the sharp curves. Gives the blind drivers something to run on.

My idea was, once I get my lathe in service, I'd turn the diameters (and probably true the wheels up--I suspect they could use it) all to the same diameter and spring 'em to suit. I can do w/o the noisemaker for now. The chuffer, or whatever it's called.

Les
 

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Discussion Starter · #17 ·
Gives the blind drivers something to run on

Les,
The other solution is to make the blind drivers very wide - more like rollers! The B&O RR Museum has a few examples.

B'mann used pins behind the wheels on their 2-6-0 to stop the wheels falling off, I believe. (I've never investigated personally, but there's a few threads here in the archives.)

You may have fun turning the wheels. I'm not sure what they are made of, but they are definitely plated.
 

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Pete,

Plated isn't a problem. If they've got plastic centers and metal tires, then there might be a problem because the inner part would turn and the outer part would want to drag against the tool bit. Hence, chatter, if not a broken center. If that is the case, they can always be ground. Just be slower, is all.

I haven't heard of wide blind drivers. I'll Google and see what I can find. That'd work, but it'd sure look funny, not to mention the crank rods and whatnot that'd have to be fitted. Ew.

Les
 

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I have seen full sized engines with wide blind drivers... some nearly twice as wide as the flanged wheel. The "excess" is equally distributed both closer to the frame and away. The side rods have to be offset (bushed out) on the other wheels to account for it.
 

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SV:

Making wide wheels would be a problem for me until I can afford a mill and indexing head. That's about $1K at Micro-Mark's prices. I cannot find a souce for spoked drivers OR freight car wheels in the sizes I need/want, other than HLW, and the ones I looked at come with axles, which I don't particularly need. No freight car wheels at that site that I remember.

I'm putting $$ aside for one of the M-M mills, as I mentioned in another thread, but it'll be a good long while yet before I get one. Got plenty to do in the meantime, howsumever.

Les
 
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