Compound/Cross Slide Interface

ddickey

H-M Supporter - Gold Member
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I know the compound is the weak link but where is it exactly? Is it where the compound connects to the cross slide?
The reason I ask is because I'd like to put a solid post on my lathe but not willing to drill and tap any holes in my cross slide. My thought was to just put a 6" x 3" piece of steel where the compound would attach.
 
Take kthe compoiund off and determin how it is secured. Then devise something better for your solid post.
 
My take on the compound slide weakness is that the dovetail/gib design is not as solid (even when locked) as a pure bolt down set up.
Plus, the travel built into the compound allows it to overhang the mounting bolts a considerable amount creating a potential for flex. I do not think that how the compound is bolted to the cross slide is the problem.
So a solid piece like you are contemplating, using the same mounting bolts as for the compound, would be significantly more rigid than a compound slide.
 
I agree with Tozguy. My Hardinge uses a pin coming up from the carriage, a cam goes through the base of the compound pulling down on that pin. Not even bolted. The solid post using the same hold down made a considerable difference.

Greg
 
Mine just has the basic 2 t bolts holding down the compound with a centering pin.
Maybe add a t bolt so there would be three. Could even machine the solid post to fit into the groove of the cross slide. Not sure if that would make much of a difference though.
 
I would save for last any modification of the mounting system to the cross slide, and then only if there is actually something to gain.
It would be so easy to over-stress the cast iron of the cross slide if you deviate from the original design. Even as is the two nuts holding the compound to the cross slide do not need to be torqued much to work adequately.
 
Several years back, there was discussion about how the compound mounts on the 9X20 machines. When the mainland Chinese entered the market, things heated up quickly because of the "softness" of the compound mounting.

The end result of that conversation was to use a four bolt mounting base, considerably thicker, with the stud mounted therein. Not the best solution, by a long shot, but do-able by any amateur (like me) with a little competance. It is nowadays being marketed on eBay, to fit the machines with two slots.

Compound ridgidity does matter. On the smaller machines, it would be anything "above" the cross slide that can be rotated. On larger machines, the same basic description applies but the mount will differ by the builder.
 
My take on this problem. Big improvement particularly in parting. I know you said no tapping but I tapped mine and it worked out fine. You just have to make sure the bottom of your block is flat so you don't torque the xslide gib.DSC_0825.JPG
 
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PM1127 uses t-slots. I made the block overhang the sides a little to help alignment and spread force over a wider area. The block is 7075 aluminum, the top plate is ground steel. 4 bolts with t-nuts in the slots to hold it on. The height was made to match the compound to ensure that the tools can be set on center.

The ridgity difference is very noticeable. I leave it on unless I need the compound for tapers. Threading I just go straight in.


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