center line tolerance.

[RVRTRSH]

We are using a turn table set up; we need to build a live center at the top to hold the parts. My question is how true to center does the part need to rotate to get a good coating? What would be a good run out? Does the part need to run out .001-.002" or is .010- .020" a good enough run out? We are spraying HVOF and have a 15" stand off. Thanks for the input.

[Gordon]

Hi RVRTRSH

I think it will depend on size and rotation speed of part and type of turn table. Never really measured run out as such, just judged by trueness or smooth running by eye and feel. I don't think the sort of run outs you are taking of here will have any significant effect on coating quality as long as things stay put. Probably more important aspect I think could vibration/shaking of equipment due to forces from rotation of poorly balanced parts.

Once saw a solid steel roll around 8" diameter by 2' long rotating at 500 RPM being plasma sprayed. I did mention while passing that I did not like the look of the set-up. Anyway about 5 minutes later the roll went into a violent fit of vibration and dropped out of its supporting centres and very luckily dissipated all that energy against booth wall and concrete floor rather than running a mock and causing harm.

[RVRTRSH]

Gordon, so a .010-.020" run out should not have any effect on the coating? I ask this because I do not wont to spend a lot of time on centers if the bigger tol. will work the same. We will be doing the grinding in house and are just trying to speed up production. Less time and abuse on the part from the grinding would be nice. We do hard chrome also and are just trying to avoid the uneven build up you get during this process. I know that it is alot worse in hard chrome than HVOF. Sorry I jumped all over the place. Thanks for the input.

[Stephen Booth]

Dear RVRTRSH

I agree with Gordon, 0.020 inch run out on the centers should not have any significant effect on the coating. More of a concern is that the center can adjust to the changes in dimension as the part heats up, and handle the higher RPM required for achieving the proper surface feet per minute of the gun vs work piece. Your traverse or gun manipulator is probably and RPM are probably more critical to the set up.

regards

Stephen

[Gordon]

Hi RVRTRSH

If we look at it this way (extreme example): + or -1" on a 15" spray distance would make only very slight difference in coating quality and geometry, while obviously the same can't be said for machining off-set with tool or grinding wheel.

[RVRTRSH]

Gordon and Stephen,
Thanks for the input.