11-07-2017, 05:33 PM
I cannot seem to make up my mind how I want to mount the little toolmaker’s vise, so I decided to drill the dovetailed plate in such a way that I can mount the vise in three different orientations. I also thought to cut down the dovetailed plate to the bare minimum required to hold the vise (to reduce a little weight). I’ve changed my mind about that as well. It’s a lot easier to remove material than to add it back so I’m going to use the thing for a while before determining a final configuration.
In the meantime, however or whatever I choose to do, I’m tired of fooling around with the #7-32 screws !!! (The Chinese engineer who specified this thread needs to repeat his human engineering class.) For the last time – I swear it – I set the lathe up for the 32 pitch threads and single pointed eight short threaded aluminum rods.
This time, since the material was soft, the threaded length short and well-supported, I didn’t require a dead center and was able to use the QC toolpost. There was plenty of access for the cutting tool so the lantern toolpost and Armstrong holder were unnecessary.
After boiling the vise and the screws for a few minutes in water with detergent, I rinsed thoroughly with hot water, dried the parts, rinsed again with alcohol and allowed to air dry. The idea, as some have likely already guessed, is to eliminate the need for #7-32 screws by epoxying the aluminum #7-32 inserts into the vise and then drill and tap them for #4-40.
I considered drilling and tapping in the lathe, eliminating a set-up in the vertical mill but I was afraid of breaking the part due to the thin wall thickness between the #7-32 minor diameter and the #4-40 major diameter.
#4-40 is a pretty small screw but there will be two, minimum, and the load for this light grinding is nearly negligible. For curiosity, I calculated the load required to shear a single #4-40 stainless steel screw (minor diameter .080 inch, yield point of 75,000 PSI) to be 377 pounds.
This would be the figure expected in ideal lab test conditions – field conditions, for various reasons, would reduce that figure by 2 or 3 times. In any event, as noted the loads are light. And if a magnetic chuck can hold work for light grinding, a #4-40 screw will have no difficulty.
I warmed the vise a bit, so that the epoxy (Loctite EA 1-C) would thin and flow well. I applied a bit to each of the eight mounting holes, screwed in the threaded inserts and allowed the epoxy to cure for the recommended 24 hours. After sanding down the protruding ends of the inserts:
I had carefully measured the hole locations before epoxying the inserts. After securing the vise in the mill (the 1-2-3 blocks are used for support only) I dialed in the locations of the holes to drill and tap #4-40 into the inserts.
As always happens, seven of the eight holes were incident-free but on the final hole, the tap broke as soon as it entered the hole. Taking a close look, the cause was obvious:
The hole location was off quite a bit, causing the tap to try to cut into the hardened tool steel of the vise. Clearly there has to be a loser in that competition. This was my fault – I measured one side of the vise and presuming that the hole pattern was duplicated on the other side, I used the same dimensions.
Of the three holes located on that side, two were correctly located and the third – for some obscure reason – was mis-located by the manufacturer. Had I noticed, I could have plugged the hole and re-drilled. Now my options are to use a carbide end mill to cut away the broken tap and repeat the plugging process or (if the gods are smiling on me) break up and chip away the piece of broken tap, which is small.
At this point, I wish that I’d at least tried to single-point AND drill/tap in the lathe, ha-ha-ha. I'm calling it a day.
In the meantime, however or whatever I choose to do, I’m tired of fooling around with the #7-32 screws !!! (The Chinese engineer who specified this thread needs to repeat his human engineering class.) For the last time – I swear it – I set the lathe up for the 32 pitch threads and single pointed eight short threaded aluminum rods.
This time, since the material was soft, the threaded length short and well-supported, I didn’t require a dead center and was able to use the QC toolpost. There was plenty of access for the cutting tool so the lantern toolpost and Armstrong holder were unnecessary.
After boiling the vise and the screws for a few minutes in water with detergent, I rinsed thoroughly with hot water, dried the parts, rinsed again with alcohol and allowed to air dry. The idea, as some have likely already guessed, is to eliminate the need for #7-32 screws by epoxying the aluminum #7-32 inserts into the vise and then drill and tap them for #4-40.
I considered drilling and tapping in the lathe, eliminating a set-up in the vertical mill but I was afraid of breaking the part due to the thin wall thickness between the #7-32 minor diameter and the #4-40 major diameter.
#4-40 is a pretty small screw but there will be two, minimum, and the load for this light grinding is nearly negligible. For curiosity, I calculated the load required to shear a single #4-40 stainless steel screw (minor diameter .080 inch, yield point of 75,000 PSI) to be 377 pounds.
This would be the figure expected in ideal lab test conditions – field conditions, for various reasons, would reduce that figure by 2 or 3 times. In any event, as noted the loads are light. And if a magnetic chuck can hold work for light grinding, a #4-40 screw will have no difficulty.
I warmed the vise a bit, so that the epoxy (Loctite EA 1-C) would thin and flow well. I applied a bit to each of the eight mounting holes, screwed in the threaded inserts and allowed the epoxy to cure for the recommended 24 hours. After sanding down the protruding ends of the inserts:
I had carefully measured the hole locations before epoxying the inserts. After securing the vise in the mill (the 1-2-3 blocks are used for support only) I dialed in the locations of the holes to drill and tap #4-40 into the inserts.
As always happens, seven of the eight holes were incident-free but on the final hole, the tap broke as soon as it entered the hole. Taking a close look, the cause was obvious:
The hole location was off quite a bit, causing the tap to try to cut into the hardened tool steel of the vise. Clearly there has to be a loser in that competition. This was my fault – I measured one side of the vise and presuming that the hole pattern was duplicated on the other side, I used the same dimensions.
Of the three holes located on that side, two were correctly located and the third – for some obscure reason – was mis-located by the manufacturer. Had I noticed, I could have plugged the hole and re-drilled. Now my options are to use a carbide end mill to cut away the broken tap and repeat the plugging process or (if the gods are smiling on me) break up and chip away the piece of broken tap, which is small.
At this point, I wish that I’d at least tried to single-point AND drill/tap in the lathe, ha-ha-ha. I'm calling it a day.