Thread: Engineering help please - flex in stainless tube and motor power required for spit

Hi Brendan,

I'm not sure if concrete would work. It spawls at high temps (although not sure if the spit would be hot enough to do this) and it may not offer much support once it cracks. You may end up with the weight of the concrete but not offering much extra in strength. WRT to the steel insert, it may not need to be an interference fit. Just a snug fit may do because it will still add strength once the SS flexes and takes up any difference in size. It would not even need to be round, square may also work and because it's only contacting at four points so still offering strength but sliding it in would be easier. The other option with round insert, drill holes in the SS at regular, measured locations and then through weld once the insert is in place (with SS electrodes) then neatly grind the weld back so you cant see it.

Just some thoughts

Cheers,

Simon

Originally Posted by 19brendan81

I thought about filling the tube with concrete to stiffen it up - what do you reckon?

Concrete has aggregate which makes it strong.You would never get the correctly evenly mixed aggregate right down the tube.I have no idea of what effect the 3 or 4 hrs of heat would have on the curing /strength. I does not seem a good idea to me.

Grahame

Here is a picture of mine, I'm the King when it comes to Spit cooking...



1. It uses a Washing Machine motor. This motor is 40 years old and still running. They don't make washing machine motors like this anymore.
2. Runs via a gear system, and also twin wheels to change speed on the fly
3. Solid spit stainless steel bar, I have done lamb (easy) and pig (heavy) no problems, no flex.

The trick is to ensure there is no slippage...i.e. the weight is concentrated at the hips and shoulders, not the middle. I support it with 3 U-bolts and wire.
Need to make sure it very very secure/tight. otherwise the body will twist (due to the torque contributed by weight) as its cooked.

As you can see with mine I have a cylinder (old hot water system split lengthwise) for the heat to be concentrated onto the lamb.
The picture above shows the first few minutes of putting it on. Soon after it changes color it is lowered, variable height easy to do while its cooking.



Let me know if you have questions.

Yeah I have gone off concrete. IM sure it was a tip I read somewhere but I no longer can see it working. I dare say it would crack up quicky and be useless.

Dean whilst triangulating may work it would make fabricating the tie off points (which need to slide up and down the bar) more difficult. If I am going to buy 6M of 6mm solid bar for triangulation I would probably prefer to buy 2m of solid bar of the correct diameter.

If I can get some solid mild steel cheaply I think i'll try insertit up the middle of the stainless....if I cant I'll just bite the bullet and buy a proper piece.

GTI - nice looking beast. I have done a few spits before and agree securing the properly is the absolute key....i'll never forget the first one we did (a lamb) which after about 1 hours cooking was thrashing around so badly we had to pull it off and try tie it down properly....no fun when the thing is burning hot.