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Attempting to weld
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Nexus
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Joined: 17 Jun 2004
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Looking for some advise on welding.
Mainly regarding steel rods for an axle.

Question is,
is it a no no to weld onto a rod that has been already hardened.
I Gather the general thing to do is do your welding and stuff and then harden the rod.

So if I where to purchase some prehardend steel for an axle do I have that ability or should I use another method to attach things to this rod?
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Post Wed Sep 22, 2004 6:27 pm 
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Knightrous
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If you have a hardened shaft and you weld onto it, beause the welder will produce near 6000`c of heat, you will infact un temper/harden the shaft. You can reharden it while it is hot by oil quenching or by air cooling. I'm not an expert on the ways of hardening, but ask Andrew, he does all the tempering and quenching in our team.
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Post Wed Sep 22, 2004 7:13 pm 
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mytqik



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You really need to ask yourself, Why do I want a hardened axle?

There are 2 main types of hardening:
1. Case Hardened. This is the option for axles. The outside 2-5mm is hardened by various means, while the centre of the shaft is left in its natural state. This allows the outside of the axle to wear really well, while allowing the centre on the shaft to withstand the shock loadings. The thing to remember is the higher the hardness of steel the more brittle it is.

2. Through Hardened: This is used more for wear resistance than strength. Things like pump impellers & the like are fabricated/cast in their annealled state & then through hardened for a longer working life. The other things that may be through hardened are lathe/milling tool tips & argicultural impliments. The problem with through hardening is that the steel can become very brittle.

Also as a footnote, not all steels can be hardened.

Back to the question I originally posed. You dont need a case hardened because I doubt very much that your bearings are going to be wearing on your axle & I also doubt that you need it for wear resistance. So my opinion would be not to worry about hardeing your shafts as it would be a waste.

Post Wed Sep 22, 2004 8:21 pm 
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Nexus
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You may be right. I never considered it for wear purposes as it wont be wearing on anything, it was more because, as the axle is only supported by one end I thought it might need hardening to make it harder to bend.

Have at the moment a shaft made out of stainless steel which I have been using to set up the robot with but have doubts it is strong enough and bend under a hit. Would rather the wheels take the load and keep the shafts straight.

So can anyone confirm if stainless steel is appropriate for an axle.
half inch diameter, 4 inch total length, 2 inches in bearings.

Or is it asking for trouble later?
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Post Wed Sep 22, 2004 10:03 pm 
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andrew



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well half an inch is about 10mm so that may be alright. steinless steel is some strong stuff though so u may be alright using it.
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Post Wed Sep 22, 2004 10:43 pm 
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mytqik



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Actually Andrew, 1/2" = 12.7mm.

Nexus, how long is a piece of string? The reason I say this beacuse the main factor in bending is the distance between were the load is applied (ie centreline of wheel) and the last support (ie centreline of bearing). What load do you want the shaft to support? Do you only have the one bearing supporting the shaft? If so what is going to stop the shaft pivoting at the bearing like a see-saw?

If you provide some distances, a sketch would be fine, I can do the maths & calculate the exact load it would take to bend the shaft for you. Also, do you know what grade the SS shaft you have is? If not, put a magnet next to it & let me know if it magnetic. This will rule out various grades. I can then take an educated guess on which grade it is.

Post Thu Sep 23, 2004 12:29 am 
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Nexus
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That would be cool if u could do that Mytqik.

Have done a pic of the layout to scale so its easy to visualise, front shaft is about 100mm and half of that is within the 2 bearings, BY the way that was a good joke about the see-saw.

http://robowars.org/forum/album_pic.php?pic_id=243

Doesnt seem to be magnetic, cant tell u anymore apart from that I gather it would work in normal conditions but dont know how Big a hit it could take or if I can take a leap and jump on its back.

Suppose it would be hard to calculate impacts from spinners as there are so many variables but I would like to think I can ride this thing aggressively without bending the axles so some theoretical calculations would be useful.

The only measurements that can be altered are that the shafts can be reduced in length slightly, did a worse case scenario.
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Post Thu Sep 23, 2004 1:47 am 
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mytqik



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Nexus, I am slightly snowed under at the moment, But I can have an answer after MM4 on the weekend.

My best suggestion, just looking at it would be to try & make the front setup similar to the rear ie: space the bearings apart, this way the bearings will distribute the forces better through your chassis.

It would also mean that your front & rear axles are the same & therefore you dont need to carry as many spares.

I am only using 3/8" or 9.525 shaft on mine & I can easily jump on mine, although my setup is slightly different.

I will have an answer ASAP for you.

Post Thu Sep 23, 2004 3:01 am 
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Nexus
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No Problemo mytqik.

IN regard to front bearings dont have the luxury for much movement.

Reason is between the front 2 axles lyes the weapon system pivoting on the same axis like an axlebot so hence my layout.

There will be considerable mounts to carry the load so not much concern there.
Yeah spares will need to be doubled as axles are different length hence thats why would like to make it so it doesnt bend that easy.

Most of the weight will be put on the back axles but there is a little mod I could do on the width of the weapon mounts that will allow me to space out the front bearings slightly but only about a half inch gap between them.

Apart from the ease to remove the bearings to access the weapon it was the oversizing of the shaft and bearings that I thought could compensate a bit for the forces involved in this setup.

Final tweak I could do is reduce the length of the shaft that extends out of the bearings to help with loads.
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Post Thu Sep 23, 2004 3:32 pm 
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Nexus
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Oops, made a small error in the pic.

The bearings are 25mm wide, not 12mm as stated in the pic.
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Post Thu Sep 23, 2004 5:16 pm 
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timmeh
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Dose anyone know where i can get some ali welded at a good price?
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Post Fri Oct 15, 2004 10:58 pm 
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