It is COLD out there but I put on several layers of clothing, surgical gloves and went out to the shop for an hour to finish up the legs. This will be the last trip until the heaters arrive !
I wanted to angle the legs out slightly from the grinder table; fifteen degrees looked about right when I tried different angles in the CAD layout. In the following photo a leg that was parted off on the lathe, is installed in a collet block. (Have I previously mentioned that this is nasty material ? The end mill is making the first pass across the end of the leg - look at the size of the burr it has raised !)
A fifteen degree angle plate in the mill vise is held in position by the vise stop, as shown. The collet block rests snugly against the angle plate as the legs are milled to length at a fifteen degree angle and piloted for 1/4-20UNC-2B perpendicular to the fifteen degree angle.
After the milling operation the 3/8 end mill was changed to a 3/16 end mill for producing a pilot hole for the 1/4-20 threads. I could have used a slitting saw in the mill, BTW, to cut the legs to the correct length at fifteen degrees but my saw arbors have larger shanks and would require a change of collets, entailing cranking the knee up and down'
The two end mills used had 3/8 shanks - no collet change required and the knee doesn’t have to be lowered/raised. The larger end mill was used to cut to length at the correct angle and the smaller end mill for a pilot hole. It's often useful to recall that plunging with an end mill, if carefully done, will always produce a straighter hole than drilling (note that a possible exception is gun-drilling) because plunging is a boring operation for all practical purposes. In fact, many of us use end mills as boring tools in the lathe.
Normal tap drill diameter for 1/4-20 would be about .201 diameter but as noted, a .201 drill plus drill chuck would require cranking the knee up/down to remove/reinstall the end mill and the drill chuck. Naturally I wanted to cut the angle AND produce the hole in the same setup so that the hole would be perpendicular to the angle.
I had no re-ground end mill to produce the right pilot hole so the 3/16 end mill was used to produce a pilot diameter that could easily be reamed out with a .201 drill, by hand. (The existing plunged 3/16 hole could have been used as-is for tapping in this soft material but why make tapping harder than it needs to be ?)
An old keyless drill chuck attached to a shop-made handle is convenient:
Hand reaming with drill
De-burring with counter-sink
Tapping
Incidentally, since I mentioned not liking to crank the knee up and down (who does unless there is "Z" axis power feed ?), I'll point out something that occurred to me many years ago. One day, after lifting the knee for about the thirtieth time, I started thinking about a way to minimize that effort.
I noticed that the typical R-8 collet has a grip length of about 3/4 or maybe 1 inch. The dim little light bulb in my head flickered for a moment when I noted that all of my drill chuck arbors were 3 and 4 inches long ! Immediately, I cut them all down to about an inch and saved about three inches of knee movement to insert and remove the chucks.
Further, I made some new arbors and shanks (for tooling that I used the most in the vertical mill) standardizing on 1/2 diameter. This covers most end mill sizes that I normally use so to change over to a drill chuck, for example, it's necessary only to drop the knee about a couple of inches because no collet change will be required - all tools for a particular task having the same diameter shank. Obviously this will not always be possible but you'd be surprised at how much less cranking (and time expended) is required.
After tapping the 1/4-20 holes, I needed to round the ends of the legs so back they went to the lathe. I used a tailstock center to support the legs because a forming tool would be used to round the ends. Forming tools exert more pressure, of course, than a normal turning tool.
Increased cutting tool pressure at the end of a cantilevered, flexible part would likely result in a scrapped part unless the part is well-supported. But one cannot cut to the center of a workpiece supported with a conventional tailstock center so a “half-center” was used.
As shown in the photo, almost half of the end of the center is ground away to allow the cutting tool to plunge all the way to the center-drilled hole in the work. (FWIW, it can be seen that this dead center is made from two different materials. The working end is carbide , brazed to the heat-treated shank and ground to dimension.)
At this point, the motor must be removed so that the ¾ inch table can be machined. That’s going to wait until I receive the space heaters and verify that they will toast my old body to a functional degree. At present this is the concept (sheet metal panel and grinding wheel guard not shown):
Cheers !
I wanted to angle the legs out slightly from the grinder table; fifteen degrees looked about right when I tried different angles in the CAD layout. In the following photo a leg that was parted off on the lathe, is installed in a collet block. (Have I previously mentioned that this is nasty material ? The end mill is making the first pass across the end of the leg - look at the size of the burr it has raised !)
A fifteen degree angle plate in the mill vise is held in position by the vise stop, as shown. The collet block rests snugly against the angle plate as the legs are milled to length at a fifteen degree angle and piloted for 1/4-20UNC-2B perpendicular to the fifteen degree angle.
After the milling operation the 3/8 end mill was changed to a 3/16 end mill for producing a pilot hole for the 1/4-20 threads. I could have used a slitting saw in the mill, BTW, to cut the legs to the correct length at fifteen degrees but my saw arbors have larger shanks and would require a change of collets, entailing cranking the knee up and down'
The two end mills used had 3/8 shanks - no collet change required and the knee doesn’t have to be lowered/raised. The larger end mill was used to cut to length at the correct angle and the smaller end mill for a pilot hole. It's often useful to recall that plunging with an end mill, if carefully done, will always produce a straighter hole than drilling (note that a possible exception is gun-drilling) because plunging is a boring operation for all practical purposes. In fact, many of us use end mills as boring tools in the lathe.
Normal tap drill diameter for 1/4-20 would be about .201 diameter but as noted, a .201 drill plus drill chuck would require cranking the knee up/down to remove/reinstall the end mill and the drill chuck. Naturally I wanted to cut the angle AND produce the hole in the same setup so that the hole would be perpendicular to the angle.
I had no re-ground end mill to produce the right pilot hole so the 3/16 end mill was used to produce a pilot diameter that could easily be reamed out with a .201 drill, by hand. (The existing plunged 3/16 hole could have been used as-is for tapping in this soft material but why make tapping harder than it needs to be ?)
An old keyless drill chuck attached to a shop-made handle is convenient:
Hand reaming with drill
De-burring with counter-sink
Tapping
Incidentally, since I mentioned not liking to crank the knee up and down (who does unless there is "Z" axis power feed ?), I'll point out something that occurred to me many years ago. One day, after lifting the knee for about the thirtieth time, I started thinking about a way to minimize that effort.
I noticed that the typical R-8 collet has a grip length of about 3/4 or maybe 1 inch. The dim little light bulb in my head flickered for a moment when I noted that all of my drill chuck arbors were 3 and 4 inches long ! Immediately, I cut them all down to about an inch and saved about three inches of knee movement to insert and remove the chucks.
Further, I made some new arbors and shanks (for tooling that I used the most in the vertical mill) standardizing on 1/2 diameter. This covers most end mill sizes that I normally use so to change over to a drill chuck, for example, it's necessary only to drop the knee about a couple of inches because no collet change will be required - all tools for a particular task having the same diameter shank. Obviously this will not always be possible but you'd be surprised at how much less cranking (and time expended) is required.
After tapping the 1/4-20 holes, I needed to round the ends of the legs so back they went to the lathe. I used a tailstock center to support the legs because a forming tool would be used to round the ends. Forming tools exert more pressure, of course, than a normal turning tool.
Increased cutting tool pressure at the end of a cantilevered, flexible part would likely result in a scrapped part unless the part is well-supported. But one cannot cut to the center of a workpiece supported with a conventional tailstock center so a “half-center” was used.
As shown in the photo, almost half of the end of the center is ground away to allow the cutting tool to plunge all the way to the center-drilled hole in the work. (FWIW, it can be seen that this dead center is made from two different materials. The working end is carbide , brazed to the heat-treated shank and ground to dimension.)
At this point, the motor must be removed so that the ¾ inch table can be machined. That’s going to wait until I receive the space heaters and verify that they will toast my old body to a functional degree. At present this is the concept (sheet metal panel and grinding wheel guard not shown):
Cheers !