i have two points (actually three) two below and one above with each a spherical positional tolerance of .050. i have a weldment that attaches to all three points but it is a fixed weldment ie. no joints. for strength and stability. the two lower points are slip fit (shoulder bolts) and carry all the load mostly. The only way I can deal with the tolerance stack up is to put an oversized hole at the top but only just enough to allow a fit. How much clearance do i give the .625 diameter pin on top? the two below are at an compound angle. if I put a line between the lower two points and the spread between that line ant the upper hole is 101.47 not that it matters - just to give some scale. thanks for any input on this and more detail is available for this question.
Hello,Originally Posted by ramming
To accommodate the positional tolerance of 0.050 and ensure a fit, you would need to provide a clearance of at least 0.050 for the top hole. This will allow the .625 diameter pin to fit within the tolerance range and accommodate any potential misalignment or variation in the assembly.
For your weldment to accommodate positional tolerance problems, an oversized hole at the top must allow enough clearance for 0.625 diameter pin to fit through without looseness; how much clearance depends upon tolerance requirements and allowable deviation; considering this compound angle has two points spread 101.47 apart between it and upper hole is 101.47 units not specified). To help provide more accurate answers you could refer to engineering standards or guidelines; additionally more precise answers could be obtained with more details provided.
It sounds like you're dealing with a precision assembly where you have to consider tolerance stack-up and ensure that your weldment attaches securely while accounting for the positional tolerances of the points. Given your setup, you're looking to provide enough clearance for the .625 diameter pin to fit through the hole at the top while maintaining stability and load-bearing capacity.
Hi ramming,
Whenever you're dealing with weldments you have to deal with distortion. This can make it difficult predict possible as-built tolerances. I'm trying to visualize your weldment. Is it something like a custom fabricated A-arm? You'll see these a lot on custom automotive and ATV suspension pieces. Sometimes they use a turnbuckle-like connection with right and left hand threads to adjust length and position. They often use Heim joint connections for the same reason. Are the two bottom attachment axes in line with each other like on a typical A-arm? If not and if they are angled to each other then the datum structure would be a lot harder to define. At any rate, in order to hit your required tolerance, if you have a good weld fixture, can fit up your connecting pieces well with zero gaps (are you using tubes as the connecting members?), are making it out of carbon steel rather than stainless, have a good welder who has lots of TIG welding experience, etc, etc, you MIGHT be able to hit your .050 tolerance. Often times with weldments, if higher precision is required you need to leave extra material for post-weld machining.
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