Dial Indicators, Vibration & Damping

[Bryan]

Does anyone know how to increase the damping on an indicator?

I bought cheap long travel one from CTC to fit to my cross slide. An Analogue Readout if you like. 50mm x .01. Works great. Until you turn the lathe on, then the needle jumps about like a frog in a sock. In a word, useless.

The interesting thing is I tried several smaller indicators - the normal 10mm ones - ranging from Mitutoyo to plastic fantastic and they are rock steady. So it doesn't seem to be an issue of quality, but one of size or design.

Anyway I'd like to find a fix as I don't know what else I'd do with an indicator with a 2 inch stroke and a face like a dinner plate. I pulled the back off but nothing suggested itself. I was hoping to see 'DAMPING + -' in big friendly letters. :whatonearth:

[Dave J]

Could it be the way it's mounted? Or can the lathe vibration be fixed?
A picture of the set up would be good to have a look at.

Dave

[Gunnaduit]

I might be showing my ignorance, but I thought that a long time ago I read not to use a DTI when the machine is on, for precisely that reason (needle will jump all about) - it is only meant to read on something that is basically static. I read that after I did what you did. I only did it once and immediately realised it was no way to treat the Starrett Last Word I had just bought back then. Highly sensitive and very accurate, but doesn't like dynamic loading. Use for truing up and adjustments etc, not as an "ARO" analogue-read-out (as per DRO). But one of the big boys will know different?

[Dave J]

Your right there in that they shouldn't be used on a job while the lathe is running.
The way he is using it is for cross slide movement which should not affect the indicator while the lathe is running, other than vibration which is what he is having a problem with.

Dave

[Gavin Newman]

I agree with Dave J, a picture of the setup would help. I have a similar setup with DI on the cross-slide and one on the ways and they stay steady even when machining.

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[Bryan]

Additional info:

The needle only vibrates when the cross slide contacts the tip.

I can tap on the mount firmly with my finger and the needle barely moves.

http://www.woodworkforums.com/members/59697-bryan/albums/lathe/6142-p4121338.jpg

http://www.woodworkforums.com/members/59697-bryan/albums/lathe/6141-p4121339.jpg

[Dave J]

Sounds like the mount is ok.
Are the gibs nipped up with a bit of drag, also is the tip in the indicator tight?

Dave

[Stustoys]

Bryan,
Is your gib adjusted correctly? I think I can see it in one of the pictures sticking out a long way. This wouldn't explain why different indicators are ok.

Stuart

[Dave J]

Just looking at your picture again, it looks like the indicator tip is in line with the gib screw. It might only be the picture but if it is you would be better off with it touching the cross slide it self.

Dave

[Bryan]

The gib setting is a compromise. It's tight at the outside, free toward centre. I've tried tightening it right up to lock point, makes no diff. Locked the carriage down tight too. Same. Tip is tight.

I don't think there's anything excessive about the vibration of this machine. I'm starting to suspect a loose fit on the plunger. The only thing I've found that stops the jitters is lateral pressure on the plunger.

PS: Dave, the tip contacts the body of the slide.

[Dave J]

Once it is touching the cross slide it shouldn't move sideways. Maybe try a bit of blue tack on the compound for the indicator tip to sit on and see if it's any different.

Dave

[Gavin Newman]

Would it be worth making a packing piece to fit between the mounting shaft and the backplate of the dial indicator to stabilise the body of the indicator in case there's a high frequency vibration being generated into the DI case.

[Metalman]

Could the problem be a resonance issue with the mount? What happens at different spindle speeds? Mm.

[Stustoys]

Bryan,
Is there a gib adjustment screw in the top tight hole in your first picture?


Stuart

[Bryan]

Stuart, there's no screw in that hole. The adjustment screw is on the other end. Why the hole is there I don't know. There's no notch in the gib so you couldn't fit a screw easily.

MM, Spindle speeds don't seem to make any difference.

Gavin, I tried hand pressure in every way possible without change, except as noted above.

Dave, result! Blutack on the tip stopped the flutters. But then the needle would keep moving as the goo squashed or stretched. Double sided tape was better but the needle would still slowly creep about .01. I thought I just needed to tune the give so I tried building up layers of duct tape. I gave up at about 10. Thinking sideways, I put a centre pop where the tip bears. Zero flutter, positive response. Perfect! It seems the soft materials worked by locating the tip, rather than absorbing vibration.

I may or may not have come up with that eventually, but Dave's nudge in the right direction certainly saved me a lot of time and hassle. Thanks everyone for your input. I appreciate it.

I hope this will improve the standard of my turning. Did you find that Gavin?

:fixed:

[eskimo]

Gavin
what is the travel length of the indicator in your pics?

[Dave J]

Stuart, there's no screw in that hole. The adjustment screw is on the other end. Why the hole is there I don't know. There's no notch in the gib so you couldn't fit a screw easily.

MM, Spindle speeds don't seem to make any difference.

Gavin, I tried hand pressure in every way possible without change, except as noted above.

Dave, result! Blutack on the tip stopped the flutters. But then the needle would keep moving as the goo squashed or stretched. Double sided tape was better but the needle would still slowly creep about .01. I thought I just needed to tune the give so I tried building up layers of duct tape. I gave up at about 10. Thinking sideways, I put a centre pop where the tip bears. Zero flutter, positive response. Perfect! It seems the soft materials worked by locating the tip, rather than absorbing vibration.

I may or may not have come up with that eventually, but Dave's nudge in the right direction certainly saved me a lot of time and hassle. Thanks everyone for your input. I appreciate it.

I hope this will improve the standard of my turning. Did you find that Gavin?

:fixed:

Good to hear, but I never meant for the blue tack to be a permanent thing, only to try. Now that you have found the source you need to find out why it's happening and where the movement is coming from.


Dave

[Gavin Newman]

I hope this will improve the standard of my turning. Did you find that Gavin?

Yep, In retrospect I should have bought the lathe with the DRO fitted but it was too much of a stretch, dollar-wise, at the time. As a compromise the DIs work well, the only drawback with my rig is having to remove the cross-slide DI when using the tailstock for drilling or using the centres. It doesn't take too long, just a bit of a nuisance.



Gavin
what is the travel length of the indicator in your pics?


The saddle DI is 0-80mm and slides on a clamp on the ways. The cross-slide DI is 0-30 mm and bears on the compound. I have a series of different length anvils that clamp onto the compound for the DI to bear against. I originally intended to use the 0-80 DI for the cross-slide but the rear of the rod fouled the splash-back so I re-deployed it to the saddle and used the 0-30 for the cross-slide.

The mount uses 2 existing M6 tapped holes in the rear of the saddle so no changes were required to the lathe.

Rgds - Gavin

[Stustoys]

Bryan,
Mine is the same. The screw head just catches the end of the gib, its easy for the head to miss the end of the gib and then you can wind the screw all the way in. No cut outs on the gibs like other machines. I find without the screw at the back the gib tightens itself when I wind the compound out, then sometimes loosens itself on the way back in until it hits the front screw. There really shouldn't be sideways/vertical movement there to upset the indicator, but if its fixed and giving good results :)

Stuart

[Bryan]

Now that you have found the source you need to find out why it's happening and where the movement is coming from.
Dave

Do I? Bugger. There was me thinking the job was done. I'm convinced the problem is radial clearance on the plunger, amplified by its length. I guess I could find a more elegant way of getting the same result I've already got. But why? :)


Yep, In retrospect I should have bought the lathe with the DRO fitted but it was too much of a stretch, dollar-wise, at the time. As a compromise the DIs work well, the only drawback with my rig is having to remove the cross-slide DI when using the tailstock for drilling or using the centres. It doesn't take too long, just a bit of a nuisance.


Gavin, I made sure mine wouldn't foul anything. The trade-off is it's further away than yours so parallax is more of an issue. It's set to cover the 50mm of radius out from centre. By sliding it along I can get out to 90-odd. With a simple mod or two I should be able to cover the whole swing with two resets. Haven't tested it with the vertical slide yet but it should work well with that too.

I know everyone loves their DROs but I'm a bit turned off because apart from the cost they sound like a major hassle to fit. I like this solution for being cheap and easy. And analogue. (Though I may go digi-caliper for the carriage.)


Bryan,
Mine is the same. The screw head just catches the end of the gib, its easy for the head to miss the end of the gib and then you can wind the screw all the way in. No cut outs on the gibs like other machines. I find without the screw at the back the gib tightens itself when I wind the compound out, then sometimes loosens itself on the way back in until it hits the front screw.

Stuart, that's interesting. My front screw fits a notch in the gib, so I assumed they all did that. But it still has some play and does a little of the self-adjusting you describe. I will try an additional screw in the rear, but it may not mean much till I can get the dovetails trued up a bit more. Will then have to either shim the gib or make a new one.

[Stustoys]

Bryan,
I meant to edit my post to say the one on the front has a cut out. I not sure but I think the gibs are to long. I'll take some pictures and see what others think.
Stuart

[Stustoys]

Changed my mind, not "to long" but needs a cut out on the gib like the front. My lathe is pretty much new, the gib is 1.25mm in at the front and .25mm out at the back. Whats the point of having a 20mm deep counter bore in the back of the cross slide if the bolt head is never in there? It wont be much of a cut out which might be why they dont bother. I'll try and measure it up next week sometime, the compound is set so I cant get the cross slide off as the light is in the way.

Stuart

[Gavin Newman]

Gavin, I made sure mine wouldn't foul anything. The trade-off is it's further away than yours so parallax is more of an issue. It's set to cover the 50mm of radius out from centre. By sliding it along I can get out to 90-odd. With a simple mod or two I should be able to cover the whole swing with two resets. Haven't tested it with the vertical slide yet but it should work well with that too.


Rather than move the DI to cater for different radii, I made a series of different length buttons or anvils that clip over the compound slide, the end of the DI plunger bears against these.

[Bryan]

Great idea Gavin. Consider it stolen.