Fitted DRO to Lathe, showed up movement

[Sunset Machine]

(02-27-2016, 06:52 PM)EdK Wrote:

(02-27-2016, 12:21 PM)Sunset Machine Wrote: , but not for general turning.

Why?  

Ed

The same reason backlash isn't a real problem. The cutting pressure pushes it back against the feedscrew and down. When line boring work on the slide, the cutting pressure goes everywhere and you should clamp.

Take a poll, it would be interesting to see how many of us use a cross slide clamp when turning. Neither of my lathes even have one.

Quick note: I bet there are Tee slots on machines with locks.

[rotorhead]

Hi All,

Many thanks for that review Andrew, it's good to hear from you, I've also been in touch with Bob of late.

I hadn't thought of fixating the trunnion, as I do use it occasionally, any clamp arrangement would also have to be disabled during taper turning.

My main reason for posting the thread, was to establish if there were others out there, whom had noticed the movement showing up after a DRO was in place.

Until fitting said DRO, I was completely oblivious to any 'floating' movement.

I had experienced the odd behaviour whist taper turning, but just put that down to the accumulated slide clearances.

I remade the bearing carrier to a closer fit in the trunnion, and made sure that the slides had the minimum clearances, which did reduce my observations of before.

I'll experiment a little more before plunging into a clamp....

[TomG]

Locking the cross slide is not something that is normally required, or even possible. In fact, I can't think of any lathe I've run that even had a cross slide lock. Like Sunset said, the pressures from the cut force the slide down and against the screw. The carriage is a different story because it floats and doesn't have a screw to hold it in place.

Chris,

When you say the cross slide moves .002", does it happen all at once, or over a distance and if so, how far? Also, your taper attachment should not be connected when you aren't using it. Most lathes have a bolt that can be loosened or removed to disable it.

Tom

[rotorhead]

Hi Tom,

On my Colchester Master the Taper Turning Attachment is actually integral.

The cross feedscrew has an extension, that is captured by two back to back thrust bearings, in a circular block that sits in the trunnion atop the uppermost and moveable slide.

The other end of the cross feedscrew is splined into the captive cross-slide micrometer dial, allowing for the feedscrew including cross-slide secured by its nut, to move relative to any taper being turned, whilst maintaining whatever feed is applied at the dial end.

There is no need to disconnect the cross-slide from the taper attachment, there is a rod extension to the base taper slide, which is clamped to the bed at whatever position, that clamp is the control and the only item needed to be disconnected.

The movement I'm seeing in the cross-slide, is in its normal axis across the saddle whilst the micrometer dial is locked, and I'm applying pressure by hand to the top of the toolpost, I can push it forward by about a thou and pull it back by the same amount, giving 2 to 2.5 thou total movement.

[TomG]

Hi Chris,

I was wondering if maybe the taper attachment was influencing the movement, but if it's unclamped, that isn't the issue. In fact, I don't think you have an issue at all. Unless I'm missing something, what you are describing is backlash in the cross slide screw and is normal, actually less backlash than normal. My Hardinge has much more than that. Remember that the DRO is reading the actual position of the slide independent of the screw, so it doesn't matter if the dial is locked or not, you'll still see movement by pushing and pulling on the tool post.

Tom

[rotorhead]

Hi Tom,

I had thought it a smallish amount, and in line with backlash in the nut/screw arrangement, but it surprised me to see such movement.

Thanks for the replies though.