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Stepperhead 2
BillTodd:
--- Quote from: philf on March 16, 2021, 03:41:46 PM ---I'm confused about the 'oval' gib too.
Surely you can't ever practically have more than a line contact with an oval gib. If it was manufactured perfectly with the correct clearance built in then it would be feasible but as soon as you rotate the gib the curves won't fit resulting in line contact.
Or am I missing something?
Phil.
--- End quote ---
I suspect a faux elipse/oval of two radii with overlapping centres
Image a circle with section cut out across the diameter the squashed.
jackary:
I wil endeavour to answer your questions about the oval gib.
The bed semi-circular groove is lower than the facing saddle semi-circular groove by a small amount creating an offset aperture between the fixed and sliding surfaces. The oval gib has a profile that closely matches but is slightly smaller than the aperture profile to permit insertion. The gib is rotated to set the sliding clearance and is then set in this position. Further rotation will lock the slides together.
The gib is anchored axially to the saddle but is free to contact both the fixed and sliding grooves. The gib urges the saddle to contact the bed flat top surface and the inner guideway surface in a manner very similar to a dovetail gib. The gib contact area will closely match the groove surfaces. I also have a design (not revealed here) that matches both grooves exactly, regardless of the offset distance.
The vertical column grooves would form a full circle when aligned but are purposely mis-aligned to form an offset aperture by the oversize first gib. A secondary gib is added below the first upper gib which can be rotated to urge the offset grooves into alignment, therefore locking the column in its slideway. The gib can have a simple oval profile or be more profiled to match the groove surfaces giving closely matching contact surfaces.
I do not think the grooves would be any more difficult to manufacture than a dovetail groove. The grooves have to be parallel, but to my mind there are no stringent machining requirements. Avoiding the adjusting and locking screws for a dovetail gib is a worthwhile simplification and avoids the point contact with the gib and the screw ends. To be able to lock the slideways over the full slideway length and return the gib for sliding contact is a bonus.
The gib makes full contact with both the sliding and fixed guideways. This makes it better at absorbing the machining forces and provides the benifit of a tapered gib without the precision requirements a tapered gib demands. I made a topslide featuring an oval gib for my Colchester Chipmaster lathe about 10 years ago and it works superbly.
Alan
Muzzerboy:
It's difficult to understand how 2 concave cylindrical surfaces can be adjusted both vertically and horizontally relative to each other while both remain in full contact with the "cam" body. Clearly such a body needs to have 2 truly cylindrical convex surfaces with an offset ie not actually oval / elliptical.
The role of the conventional dovetail is to achieve vertical and horizontal constraint, which is why it is both simple and effective. It can also be machined with simple, straight edged tools. Wear and tolerances are taken up in a simple manner and this concept can use a wedge shaped gib rather than screws, to avoid point contacts.
I see you also have a design (not revealed here) that matches both grooves exactly, regardless of the offset distance. I'd be very interested to hear more - that is what these forums are about!
jackary:
Hi Muzzerboy,
Your comment
(I see you also have a design (not revealed here) that matches both grooves exactly, regardless of the offset distance. I'd be very interested to hear more - that is what these forums are about!) means that I would be revealing what I have applied to patent without anybody signing a Non disclosure agreement. This would negate the patent claims etc before the patent is granted. So from my point of view it would not be a sensible thing to do.
WeldingRod:
Now you've piqued my curiosty! I'm guessing you are getting a low stress cylinder on closely fitted cylinder thing going here, rather than the attempted plane on (hopefully) parallel plane in a typical gib.
I saw you talked about the oval gib on PM back in 2013, but the pictures are dead (photo crud bucket). Any chance of a link to the published application, assuming its past the 1 year publication time? I can't find anything clearly yours on USPTO or Goog patent. If it hasn't published yet, no worries, my curiosity can hold out that long ;-)
Ah, sorry! UK patent. No clue what your publishing stuff looks like!
Sent from my SM-G892A using Tapatalk
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