how to hold a milling attachment on a south bend 9a square

D

dansawyer

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The question is how to lock and align an off brand milling attachment on a South Bend 9a. The compound feed has been removed leaving the mounting hole. An adapter matching the compound mounting insert is attached to the milling attachment base with a 1/2 bolt. The assembly is inserted and locked with the standard locking screws. This is stable but will not hold alignment under load.
There are two auxiliary two holes in the milling base. I would like to drill two 1/4 inch holes in the cross feed to hold the milling attachment in alignment; and machine an offset pins to fit in the milling base. The hope is if the pins are offset by 5 thousands or so they can be used to both hold the base square and make fine adjustments. Is this even practical to consider? I doubt I could drill alignment holes sufficiently accurate to hold the attachment square. After just a few adjustments the milling base is square to within a thousands. I would like to be able to hole this under use. Thanks Dan
 
Dan do you already own the milling attachment? I have a SP9A milling attachment and can draw up how that fits if it helps.
 
Yes I do. It has a 4x5 plate with T slots. The vertical movement is about 4 inches. The base came with 2 mounting holes, I drilled a third in the center to attach the adapter. I got the idea for the alignment holes by looking at picture of a cross feed for sale. It described it had milling attachment alignment holes pre drilled. From that I wondered if those holes could be used for adjustment as well.
 
I think a two firmly tightened bolts will hold the assembly from moving under load. It works for holding my 6 inch Kurt vise in the mill.
 
1/4 bolts are small for the purpose: but the SB milling attachment uses pointed set screws that around that size. The extra strength comes from the set screws having some mechanical advantage on the taper of the base.

I'm sure if you only intend to do very small depth of cut, and no climb milling, you will be fine.
 
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