Hello all, I am trying to layout my front A arms to hold a press in ball joint. I am at a bit of a dillimma as which way to go with a fit for them. As to go with either a tube that has been machined on the inside to fit the press in contact patch of the ball joint- 49.4mm or to (which is my prefference) cut a plate that will be welded into grooves on the "A" arm tubes that has a hole machined in it to fit the contact patch of the press in ball joint. The second way would give me much more of surface area welded and I think would be stronger.
Biggest question is - on either methood- how much smaller does the hole need to be machined to hold the ball joint, for example ball joint contact patch minus x thousands of an inch.
Any help would be greatly appreciated.
Thanks
Dale
-this is a non standard chassis and arms using ford thunderbird spindles-

Hi Dale,

You need to refer to the international tolerance tables for limits and fits of shafts in holes. You can find this in a copy of the machinerys handbook (or the web somewhere). The interference will be based on the diameter of the joint, for small diameter joints then the actual amount undersize the hole needs to be is very small and obviously gets larger the bigger the shaft is that you try and fit.

For UK readers, well worth spending 1.50 on a Zues tables booklet for these type of queries.

Normally you will find that you will ream the hole to the size specified in the tables. You will be looking for a medium press fit i would guess, or else you looking at shrink fitting the ball joint which will prove tricky.

Kind regards,

Darren

Dale, I think the answer to the hole size would be to measure the place where the BJ would normally fit...Im assuming they are the type with straight knurls on?..like very fine splines?....I wouldn't like to guess what the interference is on those, could be anything from 2 to 10 thou IMO, and getting it right will be important....as I'm sure you'd figured too or you wouldn't be asking..

I just looked in Stock car products catalog..lots of BJS but no hole info...good catalog, worth having though..

BTW, if the BJ body is smooth (unknurled) then I agree with Darren. It's just that most I've seen have a straight knurl finish.

Thanks for the replies, the contact patch is smooth -except for the lathe marks- so just did a remeasurment of the outside diameter of the contact patch and sent the drawing to our toolmaker at work here and left the calculations to him. If its too tight to press in in the vice then I will have to sweat it in or rework the hole and if not tight enough of a press then a couple of tackwelds for piece of mind.
Thanks again for the help.

hello dale
tell your tool maker to make it a interferance fit he will then say somthing like h6 to you thats how it will be specified in the machnist hand book
by the way this will mean its a press fit
are you sure its 49.3 mm and not 1 15/16
anyway your tool maker will sort it
good luck dave

checked with 2 sets of calipers, gave me 1.9455" (digital one) and mine gave me 49.40 mm which = 1.945
double checked before i gave him the measurement
Dale

I think you're going about it the right way.
Not that it will be applicable to your scenario, but I machine .030mm smaller than the knurled diameter of the VW BJs that I use.
Be sure you're using a bottom balljoint and not one designed for the top of a car's upright. They're totally different beasts for different applications.

No I am using the ford replacement one for the spindle lower ball joint and a 3/4 heavy duty rose joint on the top in a "factory five" style adaptor with a threaded hole instead of a tapered one.
Dale

hello dale give your tool maker the ball joint to measure because 1 15/16 is 1.9375
this might mean the hole it will be a press fit in is 1 15/16
because your ball joint is 7 1/2 thou up on 1 15/16
ie you will get 7 1/2 thou of interferance
but you must get it checked by by your tool maker
cheers dave

The tool maker at work is pissed at me for asking for a goverment job. So My neighbour who is also a machinist took my drawing and the ball joint and is going to set make it up for the correct fit.
Luckily I have nice neighbours. I see a case of beer heading his way some time soon
Dale
thanks for the help