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Why Can't I get my DTI to Repeat
- Thread starter ddickey
- Start date
Have you got another chuck you can mount to hold the work piece to see if it's an issue with the chuck or the gibs/tool post.
Stu
Have you got a magnetic base you can just mag to the cross slide temporally to check ?
That way you can eliminate the possibility of grit/swarf contaminating the bearings.
I forgot to ask if you had put the spindle in neutral and without a chuck turned it by hand to feel for bumps / grittyness in the bearings. The mass of a chuck might make any slight grit or contamination not noticeable.
Stu
Weird.
I'm not sure I'm following exactly. What precisely changes between the "not repeating" checks? I'm not clear if you are saying the high/low reading changes on each rotation or each time you remove and replace the indicator and base.
Pictures or a video might help to troubleshoot.
If the spindle taper isn't aligned with the bed ways, then the measured deflection will vary depending how far you measure from the headstock.
Get a sharpie and put a dot on the circumference of whatever chuck is currently on the lathe. Lock down your carriage or tailstock and put the mag base on that. Mark an outline precisely where you place the base, and don't move the tailstock/carriage. Rotate and position the indicator tip precisely over the dot and zero the dial.
Now without touching anything else, rotate the chuck. Mark an L and the reading at the low spot, and an H and the reading at the high spot.
Do the readings (high, low, and zero) change as you continue rotating? (Would indicate preload, bearing, or spindle/chuck issues)
If you remove the indicator and base, then put everything back in exactly the same positions as before (without moving the carriage/tailstock reference location and starting on the same dot) are you getting significantly different readings? (Can't imagine what would cause this, but will help to focus in on the problem).
This is really puzzling.
I'm not sure I'm following exactly. What precisely changes between the "not repeating" checks? I'm not clear if you are saying the high/low reading changes on each rotation or each time you remove and replace the indicator and base.
Pictures or a video might help to troubleshoot.
If the spindle taper isn't aligned with the bed ways, then the measured deflection will vary depending how far you measure from the headstock.
Get a sharpie and put a dot on the circumference of whatever chuck is currently on the lathe. Lock down your carriage or tailstock and put the mag base on that. Mark an outline precisely where you place the base, and don't move the tailstock/carriage. Rotate and position the indicator tip precisely over the dot and zero the dial.
Now without touching anything else, rotate the chuck. Mark an L and the reading at the low spot, and an H and the reading at the high spot.
Do the readings (high, low, and zero) change as you continue rotating? (Would indicate preload, bearing, or spindle/chuck issues)
If you remove the indicator and base, then put everything back in exactly the same positions as before (without moving the carriage/tailstock reference location and starting on the same dot) are you getting significantly different readings? (Can't imagine what would cause this, but will help to focus in on the problem).
This is really puzzling.
Clearly you are either aboard a ship in heavy seas or aboard a spacecraft.
Kidding. That's really weird.
Let me think a bit. Even a photo of the setup/results might help to troubleshoot.
I've seen people write DTI (dial test indicator) when they mean dial indicator. If you have a real DTI (with an arm) then I second the earlier suggestion to remove the chuck and measure the interior of the spindle taper directly. If you have an old school lever arm for a regular dial indicator assembly, that will work too. Just need something that can reach into the spindle taper.
Two possibilities: Problem goes away (indicating a problem with the chuck), or problem still manifests (bearings or fundamental spindle problem).
Something is moving. If the reference location where the mag base sits and the holders have been completely eliminated, then it must be the object being measured that's moving. Removing the chuck will eliminate one more variable.
Two possibilities: Problem goes away (indicating a problem with the chuck), or problem still manifests (bearings or fundamental spindle problem).
Something is moving. If the reference location where the mag base sits and the holders have been completely eliminated, then it must be the object being measured that's moving. Removing the chuck will eliminate one more variable.