Measuring axial runout on a tube

[Jayfaas]

Hello. We recently decided to look into our own tube forming machine for our processes, and one of the features we need to measure is axial runout to ensure the cut is straight so it doesnt affect friction welding.

• One issue I see with that the wall thickness of the tube is 1.5mm, therefore if we use a cone, you barely have enough room to set a lever indicator on that surface.
• If you do not use a cone, how do you hold the shaft straight? I would assume 2 sets of wheels, but then what keeps the tube from walking?
• If you set it against a backstop, the axial of the side against the backstop is going to influence the axial on the other side, so how does one do this accurately without influence from the other end? With a small tolerance of 0.15mm and a small surface already, every little bit helps.
• I need to find something fairly cost effective but also easy enough to set up for temporary laborers who are likely not yet technically savvy enough to use a more sophisticated method. A CMM can be used for PPAP, but cannot be used as the main gauge because of capacity and lack of support on off-shifts.
• Currently our best system is a Jenoptik Opticline 1214, but even that is used elsewhere in the plant so its not efficient to use that and I'm not yet confident in the method because of the little amount of space we have to measure. We were getting errors with "too few points measured" usually indicating that it cannot see enough of the edge to make the measurement. Also with the tooling having a tapered fit, we have encountered it many times where someone doesnt install the tooling in the top good enough, and the tooling along with the live center fall out. Therefore even the Jenoptik, while a great machine, is teetering on the line of not being feasible to run in our production setting.

With such a big window for error, I fear this might be a capability nightmare, so having a good measurement system is going to be key here. Any thoughts?

 

[Jen Kirley]

Hello Jayfaas,

How long is this tube? What is the inside and outside diameter? How many of these parts will need this inspection?

My understanding of measuring runout is as simple as described here. But if the tube is very long the method shown won't work.

 

[John Predmore]

I need to find something fairly cost effective but also easy enough to set up

You said you want to check the cut is straight. Do you mean a saw cut? Do you even need runout to check the cut surface is straight? My easy-to-setup, cost-effective idea is to lay the tube in a V-block on the table of an optical comparator. (I have no idea how long the tube is.) There would be no force to cause the tube to walk. If it is not clear with the naked eye the direction of the cut, inspect once in the V-block, then rotate 90 degrees around its centerline and inspect a second time.

 

[Jayfaas]

Hey all. Thank you for the responses. The tubes can be anywhere from 400mm to 1600mm. They may vary from 40mm diameter to 85mm diameter, and thickness can range from 1-2mm. The comparator method would likely work, and that is essentially what we would be doing with the opticline, however I am trying to determine an alternate form of measurement if that machine is down or in use.

I was thinking this morning that if you put it against a big enough backstop to cover the diameter, and something to hold it straight, then maybe the axial on the end against the backstop will have minimal to no influence on the end you are trying to measure. The problem is getting a setup that is easy. For those who work in Metrology or have experience, setting this up and using a lever indicator may not be so difficult, but here we are relying on temp-to-hire workers, so I am trying to come up with something as a good alternative. Thats always the issue with alternative gauging lol

 

[John Predmore]

Here is another simple idea. Stand the tube on the cut end on a surface plate, leveled. If the tube topples over, suspect the cut end is not square to the axis. Shine a flash light where the cut end stands on the surface plate; if light shows an uneven gap, suspect the cut is not straight. If the tube stands on end, place a level against the tube to check it stands at a 90 degree angle. If you cannot get a good read with a level, hang a plumb bob from the top of the tube and look for an angle between the tube and the string. That will also tell if the tube is bent.

 

[Jayfaas]

This would be a reasonable method if we were doing it for reference, but in our case we will need variable data that is documented, and will need a measurement setup that can be put at the location of the machine on the production floor. Thank you for the response.

 

[ShadiestWesley]

Do you have a lathe you can use? For the limits specified in this case any rotating chuck should be perfectly adequate to check axial runout

 

[Jayfaas]

unfortunately not for production.

 

[Welshwizard]

What about an engineers square and feeler gauges say in 4 positions around the tube circumference? Mark the tubes and number the measurement points if you need to?

 

[Jayfaas]

Thanks for the response. I would need to have variable data, and the tolerance for the axial runout at the end of the tubes (which are only 1.5mm thick) is 0.150mm, so your method would be okay for a generic reference check, but for what they are asking here, we would need something more accurate.