What is going on - help

[colinh1301]

I have a small compact tractor and the gear stick came off in my hand today. Its a simple "L" shap bar which was welded on to a gear linkage. There is no signs of corrosion the weld just came apart. looking at it, it was more like it was soldered than welded - no real penetration. I have a clarke 150A mig welder with normal bog standard wire which I have used succesfully lots of times on steel.. The gas was flwing freely - I think it was the mixed gas but it mig have just been CO2 I cant remember which bottle is fitted. I claned up both bits of metal with the grinder prior to welding. When I tried to weld it just sort of burnt really brightly. Blobs of weld sort of came off and continued to burn really brighlty on the floor ( it reminded me of chemistry at school when you burnt magnesium). The weld just wouldnt take at all.

I dont know if it makes any difference but the wire was right at the end of the drum and ran out.

I'm not sure what the gear linkage is made out of - it looks just like steel to me.

I would relly like to get this sorted tomorrow (day off) so your help would really be appreciated.

My plan be is to drill and tap it and secure with a bolt. Can someone explain what the relationship is between the required hole size for the various metric threads are.

Cheers
Colin

 

[malcolm]

Could you post a photo of your attempt to weld the thing - that might give some clues.

For bolting what size bolt would you want to use?

 

[rtbcomp]

Try it with a magnet.

The burning blobs sound like mazak (monkey metal), an alloy of zinc, magnesium and aluminium.

http://aluminium.matter.org.uk/aluselect/01_applications.asp?alloyid=8

 

[scarecrow]

you could try a spark test on it this might give you a clue
if you tell me what size and bolt you're using I can give you the drill size for that tap

 

[Paul.]

Easy way to find a tapping size for a metric thread, Dia of bolt minus pitch, so an M6 x 1 is 5mm, or M10 x 1.5 is 8.5, and so on

 

[brightspark]

thread chart

tapping and clearance drill sizes

 

[colinh1301]

Thanks for all the info. I have a sneaky feeling it is going to be some sort of alloy like mazak. It says in the data sheet the it needs to be resistance welded - what is it, will I be able to take it too someone or would it be better to buy a replacement part?

Thanks for the help with the tapping - I have a feeling thats the way I'm going to need to go.

Cheers
Colin

 

[cutandshut]

Are you sure it's not galvanising causing your problems.

 

[colinh1301]

My inital thoughts were it might be somesort of coating so gave it a really good grinding but it will not take a weld at all.

 

[Paul.]

Some gear levers are flash butt welded, or friction welded where the lever arm joins the pivot ball, a picture may help us.

 

[colinh1301]

There isnt much left of the original weld but I will take some photos tomorrow (the tractor is down my field which is 10 miles from mt house!!)

Cheers
Colin