Author Topic: Topslide turning question  (Read 374 times)

Offline Allen Smithee

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Topslide turning question
« on: July 28, 2019, 09:16:21 AM »
In my recent task (documented in my "not a model engine" thread) I was making a part from 303 stainless bar, and the part has a 13.5deg tapered feature which I produced by swinging the topslide to the required angle.

While doing the tapered bit I noticed I was getting this "stepped" finish. It's visual only - I can't feel it with a thumbnail or see it move the needle on a DTI. I've seen it before - I only ever get this if I'm advancing the tool with the topslide (something I have no option about when turning a taper). Is this because the gib needs adjusting (can't feel any play) or just showing that the topslide isn't as stiff and so when I turn the handle (it has a ball-handle rather than a wheel, like most Myfords) the minute extra force pushing the handle at the top and the bottom is appearing as a tiny movement in the tool bit?

AS
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Online Jasonb

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Re: Topslide turning question
« Reply #1 on: July 28, 2019, 12:37:26 PM »
It can happen if the topslide is advanced by using the handle as the up-down-up movement can raise and lower the slide. Best practice is to use both hands on the rim of the handwheel and aim for a continuous smooth feed.

Offline Ian S C

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Re: Topslide turning question
« Reply #2 on: July 28, 2019, 12:47:43 PM »
You might notice a similar effect when facing the end of a bar, as you go in to the centre the speed in ft per min(or what ever) reduces, ideally as you wind in the spindle speed should increase, same happens on a taper, the cutting speed is constantly changing. (well that's my theory any way).
Ian S C

Offline Allen Smithee

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Re: Topslide turning question
« Reply #3 on: July 28, 2019, 05:54:00 PM »
No, I think Jason has it - I need to practice feeding the topslide without yanking it up an down". Facing and axial cuts using the saddle wheel are all perfectly flat; this effect is only evident when advancing the tool with the top-slide.

AS
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Offline Florian Eberhard

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Re: Topslide turning question
« Reply #4 on: July 28, 2019, 07:23:23 PM »
No, I think Jason has it - I need to practice feeding the topslide without yanking it up an down". Facing and axial cuts using the saddle wheel are all perfectly flat; this effect is only evident when advancing the tool with the top-slide.

AS

I am rather thinking that the topslide might have a not so good geometry (anymore?). If the guiding faces are like a banana, you will get the impression that the gib is adjusted properly but that is only right for one spot and therefore the topslide might wiggle because the guiding faces. If its actually like that, all you can do is overhaul the guiding faces.

Florian

Offline ChuckKey

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Re: Topslide turning question
« Reply #5 on: July 29, 2019, 08:59:01 AM »
Have you tried adjusting the gib? I take the screw bracket off and adjust for an action that might be described as only-just-not-stiff or smooth-but-only-just-does-not-bind.

George Thomas observed that the round screw points in coned dimples is not the best arrangement, and added a locating dowel and a locking screw; modifications I intend to carry out, sometime.   

Offline Zephyrin

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Re: Topslide turning question
« Reply #6 on: July 29, 2019, 10:24:01 AM »
IMHO gib strip need some adjustment, as the stepped traces you see follow the thread of the screw, owing to a nut of the slide not exactly centred...
but if it is visual only, moving the hand wheel with both hand as recommended by Jason would fix that. 

Offline Allen Smithee

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Re: Topslide turning question
« Reply #7 on: July 29, 2019, 10:53:02 AM »
1. The topslide gib is adjusted to be "firm", and there is no perceptable movement (measured with a DTI on the tool) if I apply firm presses up/down and left/right on the handle

2. The visible traces form concentric rings, not a spiral.

Clearly something is moving or flexing somewhere, so I guess I'll have to go through each part (topslide, cross-slide, saddle) and try to confirm that it's flex and then (as Jason suggested) just improve my technique.

AS
Quidquid latine dictum sit altum sonatur