Help with dropped tube axle geometry

[steelnett]

I'm collecting up parts to fabricate/build a dropped tube axle....

Starting to get me head into it and i need some pointers on some of the

geometry !!!!!

See below, i've posted some rought sketches, which, i think explains what

info i'm after............hope its self-explainatry.



Pic A

I've purchased Speedway 49-54 Chevy stub-axles and as far as i

can measure looks like king pin angle sits at 6 degree, is that correct?

If not can anyone advise ?



Pic B

What camber angle is usally built into commercial built dropped

tube axles ? ie what angle shoud i build into the beam axle?




Could any of you guys help with any suggestions

Hope you get what i'm on about and the questions are not too nieve.

I'm gonna have a load more questions as work progress, hope someone

willing to advise.

see pics

thanks for looking

Rob

 

[RPM]

I have built several axles for some of the guys here and for myself. The hardest part is getting the bends in the axle the same from side to side. Machine the ends you are going to use and mount them with the king pins into the spindles. Using large pcs of angle and a spacer, I jig the spindle up with the c/l parallel to the c/l of the axle adusting the height as needed with big shims. When you get it all aligned correctley, and all the angles right, tack weld it and then weld it solid. Kinda hard to explain with just words. I use a digital level that reads to a tenth of a degree to align everything. If you don't have a lathe I can make you some ends.

 

[der Spieler]

The CCR plans call for 9 degree camber (pic B) and 30 degrees of bend in the axle for a 4" drop. (Axle is 50" eye to eye.)

Question for RPM. The CCR plans say to make the 30 degree bends with a mandrel bender. I know a mandrel bend looks prettier but by stretching the outside wall doesn't that make the wall too thin? All of the major sanctioning bodies say no to mandrel bends in roll cages for that reason. Shouldn't an axle be made as strong as possible?

 

[RPM]

The CCR plans call for 9 degree camber (pic B) and 30 degrees of bend in the axle for a 4" drop. (Axle is 50" eye to eye.)

Question for RPM. The CCR plans say to make the 30 degree bends with a mandrel bender. I know a mandrel bend looks prettier but by stretching the outside wall doesn't that make the wall too thin? All of the major sanctioning bodies say no to mandrel bends in roll cages for that reason. Shouldn't an axle be made as strong as possible?

The CCR plans are for Ford spindles, I think he said he had Chevy spindles. They are different. I am not sure but I think 6 deg is right. I just use a tube bender to bend it. I use 2" tube with a 1/4" wall very heavy duty.

 

[Tbucit]

I made my first axle using the CCR plans and found that it was a little too wide for me. And the plans are for ford spindles as Ron said. After mine was bent I set up on a mine and cut the notch at 9 degrees.


Randall

 

[Rick]

Hmmm Totals manual says to build them with an 8 degree angle.BUT thats with there axle 13/8 od tubing.The clasic axel is a Mr.Roadster style and it has a more dramatic drop so the angle will be different.

 

[GAB]

For whatever its worth, I asked Keith Bond, who runs Super Bell for Pete & Jakes, about the official Ford word on king pin angle recently. He told me that the axles were made with a 8 angle and the spindles were made with a 9 angle which makes for a 1 positive wheel camber angle when clearances are fresh. This is for Ford, the Chevrolet is different as far as angle goes.

I would suspect that it is done for the same reason that toe-in is specified rather than toe-out. According to Hunter Engineering, who makes a lot of front alignment equipment, by starting with some toe-in as the parts begin to wear the wheels will get closer to parallel which is the desired geometry.

Just a word about mandrel benders...Most of what you might encounter in small fab shops are not mandrel machines. They are either draw benders or compression benders. Mandrel machines are generally large machines (read that $$$$) that are setup for serious production. The tooling is very pricey also.

What makes a mandrel machine is piece of tooling that supports the inside of the tube at the point of bend. This can be in the shape of just a slug of the right diameter, a bullet shaped insert that supports the outside wall of the bend part of the way, or a ball mandrel that is kind of like a big key chain that follows the bent tube well past the point of bending. These are hydraulically extracted from the tube after bending. Mandrel machines are what are used to bend thin wall tubing such as used in exhaust parts. The average race or street rod shop can't bend exhaust as the thin wall collapses if not supported by a mandrel. It is kind of backward from what most people think. The heavy wall stuff is better to bend than the light stuff for the type of benders that most fab shops have.

For a tube to be bent, the material on the outside of the bend has to stretch or thin to some degree and the inside will compress or gain in wall thickness. There is a neutral line where it is neither compressing nor stretching and most benders find that to be about 1/3 of the way from the inside of the bend. It makes it fun calculating amount of material used in a bend.

Most bends made with a draw or compression bender will form the tube into a kind of a modified "D" shape in the middle of the bend. Take a bent piece of tube and circle the middle of the bend with your thumb and index finger and then rotate them around the tube. Do you feel the shape?

Sorry for the rant, but the mandrel thing is one of the most misused terms in amatuer and small shop metal fabrication.

 

[steelnett]

Thanks everyone for the response, really has helped

GAB saying Ford Axles at 8 deg and spindles at 9 deg to make 1 deg positive makes sense.
So if my Chevy axles are at say 6 deg to achieve 1 deg positive i need to build in 5 deg on the ends. Think that sounds right. Read somewere that Speeway supply Chevy axles to give 1.25 deg positive camber, so i could check that out and adjust to suit....

RPM.......Your set up method comming off centre line of axle and centre line of stub axle spindle, using a digital level to achieve camber makes sense. I'll do it like that :lol:....Thanks for the offer to make up some ends, but i'm O.K. I've got the use of a engineering workshop, which helps..

Brilliant response from you guys, thanks again and keep up giving out good advice.

 

[steelnett]

Just getting to the point to weld on my batwings...

Sorted and lookin good...

Thanks
Rob

 

[oldtman]

I.ve got an old beat up 47 ford 3/4 ton flat bed farm truck with a 53 lincoln Y block. I was thinking of cutting it down Rat rod style. It's cold up here and wanted something for the colder weather. Has anyone used mid 70's ford pickup spindles. brakes. etc. ? I got a setup for free and was thinking of using them. either build a new tube axle or adapt them to the truck 2 springer I beam.

 

[Ted Brown]

The reason for 1 positive wheel camber angle is so that when you put all the weight on the finished axle (ready to drive) the axle flex will then make up for this, same with toe in, when you drive, the tires pull back and then things are in the correct driving position. Many times when you are all finished and take your ride to the alignment shop, they will have to bend your tube or I beam axle, to make everything fall into correct alignment.