Small Turning Job

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bikenstock
Posts: 6
Joined: Sat Nov 07, 2009 10:16 pm
Location: Tucson, AZ

Small Turning Job

Post by bikenstock » Sun Nov 08, 2009 5:21 pm

Hello folks:
I am new to the forum and am thinking about learning machining for home and hobby use. Meanwhile, I am in a project of building a 3-wheel adult trike. I need axles turned for the hubs of the 2 front wheels.

I think the ideal material would be 1" round 4130 Chromoly tubing with .25" walls. I may try a couple the same size in mild steel as well (depending on the price you quote). Online Metals offers both and I could provide both if you do not stock them.

They are about 6" long, with the first inch staying 1" in diameter and the last 5" turned down to 20mm to fit ball bearing races in the hubs. The 1-inch end will eventually have 1" thin-wall 4130 welded to it (by me). I would provide exact dimensions in a drawing made in PC Draft.

There would be a slot turned in the end of the 20mm section, .125" from the end, to hold a c-clip.

I could send the hub along for you to check clearances; it is nominally 20mm.

I can send a drawing to your email or snail mail address. If anyone is interested, you can e-mail me at bikenstock@hotmail.com Thanks and I'll await your word!

Sincerely,
Don French
Tucson, AZ

Harold_V
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Location: Onalaska, WA USA

Post by Harold_V » Mon Nov 09, 2009 1:23 am

bikenstock,

Welcome to the forum.

I suggest you review your idea of welding on a finish machined part. I would expect some distortion, which may defeat the purpose. I have no problems with the idea of welding prior to machining, assuming your choice in chrome moly isn't beyond 4130.

Depending on the design, I'm not sure I'd trust mild steel.

If I misunderstood your procedure, and the welding will come first, you have a better chance of success.

Harold

bikenstock
Posts: 6
Joined: Sat Nov 07, 2009 10:16 pm
Location: Tucson, AZ

Post by bikenstock » Mon Nov 09, 2009 12:59 pm

Hi Harold:
Thanks for the suggestion. Here is a crude first draft idea of how the turned axle will be used. I hope this is able to be seen (I am trying to send it as an attachment).

I can't see how this could be welded first. Even if a guy had a lathe with a large swingover, would one want to turn the axle with the kingpin already attached? I am not doubting your suggestion, I just don't know, I am new to both machining and welding, with my shop experience having be mainly in woodworking.

If you feel the weld would distort even 1" crmo tubing w/ 1/2" bore (hence .250" wall), I can believe that, especially anticipating how long it would take for me to do the weld as a newbie. I would say commercial makers turn the axle first then weld, but they have pro welders and perhaps go through many iterations to get it right.

So I am open to all ideas. Thanks again for trying to help and thanks to those who have already replied via e-mail (and agree with Harold that welding a turned piece is asking for trouble).

Sincerely,
Don
Attachments
TrikeHub3Web.jpg

Harold_V
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Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Post by Harold_V » Mon Nov 09, 2009 3:19 pm

There's going to be considerable force on the weld, and it's almost guaranteed you'll get distortion in welding. Assuming the project was mine, I believe I'd explore heat treatment after assembly, then finish machining. Overall, I think I'd explore a different design, so the bending force wasn't concentrated at the weld. (Do consider that I'm not an engineer).

Unless the king pin is exceedingly long, there's no reason why the piece can't be machined afterwards----then finish ground for size. That way you'll get reliable sizing for the bearings. The diameter could be turned, but with the king pin already attached, you may have to counter balance the driving plate to keep vibrations to a minimum. That wouldn't be an issue on a grinder, because you could run the spindle slow. You'd struggle with surface finish on a lathe with slow spindle speed.

One could rely on the bore of the tubing to be used as centers, with just a minor amount of machining to generate a 60° angle in each end of the tube. The king pin could act as a dog, to drive the part while being machined.

Just a thought.

Harold

jutz
Posts: 49
Joined: Sat Nov 25, 2006 2:27 pm
Location: Austin, Texas

Post by jutz » Mon Nov 09, 2009 3:37 pm

Harold,

Weren't you the one who told SealKiller about reverse boring? Seems to me this would be an excellent use for that skill. At least that's how I would do it.

bikenstock
Posts: 6
Joined: Sat Nov 07, 2009 10:16 pm
Location: Tucson, AZ

Post by bikenstock » Mon Nov 09, 2009 5:48 pm

Wow, you guys!
Can you all just move in next door to me and bring your shops! :-) Barring that, I had a simple thought too:

What if I run a piece of .500 rod through the bore of the turned axle, say an aluminum rod so I can't weld it to the work, and let that help hold the shape? Assuming the aluminum wouldn't sink too much heat away from the joint.

I am attaching a photo of the commercial trike I am trying to copy, maybe to give you all still more excellent ideas. I really appreciate the help!

Don
Attachments
HubPhoto3Web.jpg

Harold_V
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Location: Onalaska, WA USA

Post by Harold_V » Mon Nov 09, 2009 9:03 pm

jutz wrote:Harold,

Weren't you the one who told SealKiller about reverse boring? Seems to me this would be an excellent use for that skill. At least that's how I would do it.
That could present its own set of problems. The length of the cut is quite long, so unless a large boring head was used, the bar would be quite slender, yielding chatter. Not suggesting, not for a moment, it won't work, but it could prove interesting.

To your credit, after welding, the angle may not be as desired, so a correction could be made on the included angle.

Cutting the required groove would be challenging unless a facing head was at one's disposal, but, considering there would be but two grooves to cut, it could be done by hand turning the head, advancing the grooving tool after each revolution of the spindle. Any port in a storm, or so they say.

My suggested method of using the tubing bore as a centerline could prove to be not such a good idea unless the weld was accomplished with a decent fixture, and in the proper sequence to avoid tilting the part. In any case, distortion from welding would be a concern, and it's sure to happen.

Looking at the picture that has been posted, I get the idea that the housing does not include the shaft. To me it looks like the shaft is shouldered and is inserted in the welded assembly. Could be wrong. However, if I'm not, that job's a piece of cake. Weld the angle, bore after welding to create proper alignment and desired angle, then make the shafts to fit.

Harold

Harold_V
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Post by Harold_V » Mon Nov 09, 2009 9:10 pm

bikenstock wrote:Wow, you guys!
Can you all just move in next door to me and bring your shops! :-) Barring that, I had a simple thought too:

What if I run a piece of .500 rod through the bore of the turned axle, say an aluminum rod so I can't weld it to the work, and let that help hold the shape? Assuming the aluminum wouldn't sink too much heat away from the joint.
While it might help in establishing proper orientation, nothing you can do will eliminate stresses that are developed in the welding process. Sequence of weld, and the amount of weld applied will influence the attitude of one part as it relates to the other, even if the part is assembled in a rigid fixture. You are pretty much assured of some movement, including the precision diameter going out of round. To not experience the problem would be unusual.

I'm not convinced the part you showed is made as you suggested. Please read my comments in the response to Jutz. If I'm wrong, please correct me.
By changing your approach to the job, it can be made easily, assuming you can find someone with a mill and lathe. A cylindrical grinder would be a definite plus, but the job can be done using only a lathe. Bearing fits are rather restrictive, so it would require careful attention, but certainly doable.

Harold

bikenstock
Posts: 6
Joined: Sat Nov 07, 2009 10:16 pm
Location: Tucson, AZ

How The Part is Best Made

Post by bikenstock » Mon Nov 09, 2009 10:32 pm

Hi Harold:
You may well be right that the part is made other than I have thought. In light of your legitimate concerns, I am thinking of doing a "back to the drawing board" on it.

I understand you to be saying, "Make the 1" diameter, shorter cylinder, do all the welding to it, then bore a 20mm hole, maybe with a taper, into it after welding. Then turn the 20mm cylinder either from tubing or solid stock, bore it through if needed, and press it into the 1" piece." Does that summarize it? Did I miss needed details?

I wonder if there are long, 20mm drills reasonably had. I'll check Enco, Reid and McMaster and any others you suggest.

Need to think awhile. Thanks!
Don

Harold_V
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Joined: Fri Dec 20, 2002 11:02 pm
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Re: How The Part is Best Made

Post by Harold_V » Tue Nov 10, 2009 12:02 am

bikenstock wrote:I understand you to be saying, "Make the 1" diameter, shorter cylinder, do all the welding to it, then bore a 20mm hole, maybe with a taper, into it after welding. Then turn the 20mm cylinder either from tubing or solid stock, bore it through if needed, and press it into the 1" piece." Does that summarize it? Did I miss needed details?
That's pretty much what I was thinking.
A taper would be troublesome, so don't go that direction. Making the taper on the shaft isn't a problem, but it would be a nightmare creating the desired taper in the bore, and it won't really serve a useful purpose.

By having a shoulder on the inside end of the pin, it can't go anywhere once installed. A slight press fit (.0005") to insure it doesn't rotate would be a good idea, and the C clip or retaining ring you have planned would insure the axle stays put once the wheel is assembled. Not a bad design in the scheme of things, and a lot easier to build.

It might be desirable to be able to control bearing preload, depending on the type of bearing you choose to run. That would require a threaded end on the outside, with no ring groove. That way you could use bearings that provide side loads, which are likely to occur when turning corners. Just a thought.
I wonder if there are long, 20mm drills reasonably had. I'll check Enco, Reid and McMaster and any others you suggest.
Don't even think about drilling. This would require boring if you want acceptable results. Drills don't yield straight or round holes, which would be important in this case. What you need to do is make the acquaintance of someone that does machine work and explore how these things are done----then it will all makes sense. You start with a drill (if needed), but undersized. The hole is then machined by a boring tool in a boring head, using a mill. The end result is a very round and straight hole, and, assuming the operator has the requisite skills, of the proper size. Once the bore is established, the face would then be surfaced so it was at a right angle to the bore. There's more to this seemingly simple project than may be apparent to you. (I'm assuming you'd like it done properly).

An alternate to boring would be to ream, but even reamers can yield questionable results. I avoid reaming in almost all instances except for their use in installing dowel pins. You'd still have the problem of facing the end if you reamed, so it's not a real solution.

I don't want to discourage you in any way, but I would encourage you to explore machining a little more before making some of these decisions. You may save yourself some grief, and even end up with a superior job. There's a lot at stake when you consider welds that may not be up to par. I'm assuming you aren't a weldor by vocation. I've taken a couple years of welding and I'd be a bit apprehensive about welding on those parts. It's too easy to end up with welds that have no integrity.
Need to think awhile.
Good idea! And, don't hesitate to run more ideas past us. There's some very talented and skilled people on this board.
Thanks!
You're welcome, Don. Hope some of these things are helpful (and not discouraging).

Harold

Russ Hanscom
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Location: Farmington, NM

Post by Russ Hanscom » Tue Nov 10, 2009 5:34 pm

Might I suggest a step back and set some parameters.

There are options available for quality and accuracy ranging from high end to chinese/walmart. Go too high and you will price yourself out of the market, go too low and get equally poor results. As an occasional designer, I find the rush to fabricate without completing the design is too common.

Try to establish the needed accuracy/tolerances for the bearing bores, welded angle, etc, then determine the processes that give you those results. I am thinking that stesses might be low, but I could be wrong. Any calculations been made or are you relying on the competition's design? Another items is how many are you going to make? Making a deluxe one for yourself would be a totally different process than going mass production.

My shot from the hip is that turning the shaft first and allowing for distortion of the angle is probably adequate for the intended purpose. I doubt that many , if any bike manufacturers do post weld machining.

bikenstock
Posts: 6
Joined: Sat Nov 07, 2009 10:16 pm
Location: Tucson, AZ

Design Parameters and Copying the Trike Axle

Post by bikenstock » Wed Nov 11, 2009 2:43 pm

Hi Russ:
Good points all. I just got the hubs that these axles will be made for today. The stresses, without getting all "mathy" on you :-) are those of a 300 lb. rider on a 40 lb adult trike going as much as 30 or 40 mph. There are vertical loads and side loads and maybe others. Having all my engineering firmly in the seat of my pants, I am unable to provide a single figure . :?

The "competition" consists of my own commercially made trike, which I am copying where I can, and many other manufacturers of similar items. Other sources of info include many websites and downloadable DIY manuals ($) that I have looked at and/or purchased.

For instance, the axle size on my latest version is .500 inch in diameter, which is a standard size for racing wheelchairs. The 20mm hollow axle on my first design is a standard for downhill-racing mountain bikes.

A version of my latest axle design effort is found in one of the DIY manuals, in which the builder used 5/8" bolts, welded bead to them to raise two bearing surfaces and ground those down crudely with a flap disc to approx. 20mm diameter to fit the hubs. He has no lathe or even drill press, but allows that you could turn the welds down and turn the rest of the bolt between head and threads down to 1/2" if you have access toa lathe. He says it works well and a number of his readers have copied his method. So, many of my design parameters are gathered from anecdotal sources.

I have no plans to build trikes commercially. Right now, my goal is to build one "deluxe" for myself. I may purchase a lathe and try my own hand; for the moment I am looking for real machinist help and several have responded. I hope to post an amended drawing soon.

Thanks for the parameter suggestions!
Don

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