What's new
What's new

old southbend instructional video - cutting taper

Good vid thanks, I am glad that they had to make adjustments and tweaks to the taper attachment to get the taper right. I thought it was just my machine! Also I found it curious to cut the sharp taper with the compound in a pulling motion set up on the left side of the cut area. I never use my compound on that side of the piece but I haven't cut many tapers. I use the compound for mainly cutting threads. Makes sense of course but it just caught my eye since I don't use my machine that way.
 
Newtons third law, "For every action there's an equal and opposite reaction". For machine tools you'd subtract that reaction from the machines own mass, rigidity and resistance to those forces. Once you do understand everything we have or use is in one form or another basically rubber you can then start to appreciate why machines require minute adjustments to help compensate and offset those forces. Trying to exactly duplicate a taper using a test indicator against an already known taper such as a Morse Taper on the top slide or taper turning attachment only gets you fairly close. The lathes own non optional clearances and rigidity are always working against us.

Even if you could somehow preset the angle to millionth's of an inch in accuracy it would still be wrong under those actual cutting loads and conditions as those clearances and machine tool part deflections are taken up. Visualize the necessary few thou clearances between the two halves of the top slide dovetails. As there taken up under those cutting loads the slide will take a slightly different angle as the end closest to the cutting tool is jammed against the dovetail and the other end pivots in the opposite direction. The same to a lesser amount because the parts are a bit more rigid happens with the taper turning attachment as well. It's also why light finishing cuts are more accurate because the cutting loads and machine deflections are much less. It's also why cutting a male and female taper using the exact same top slide angle still won't perfectly match each other because generally the cutting forces are acting in opposite directions on the top slide as each taper is cut. Using the cutting tool upside down and cutting on the back side of the female taper can help duplicate the same loads as what happened while cutting the male taper. It's simple physics, but not quite as obvious as it would seem because it's happening at levels that can't easily be observed.
 
Newtons third law, "For every action there's an equal and opposite reaction". For machine tools you'd subtract that reaction from the machines own mass, rigidity and resistance to those forces. Once you do understand everything we have or use is in one form or another basically rubber you can then start to appreciate why machines require minute adjustments to help compensate and offset those forces. Trying to exactly duplicate a taper using a test indicator against an already known taper such as a Morse Taper on the top slide or taper turning attachment only gets you fairly close. The lathes own non optional clearances and rigidity are always working against us.

Even if you could somehow preset the angle to millionth's of an inch in accuracy it would still be wrong under those actual cutting loads and conditions as those clearances and machine tool part deflections are taken up. Visualize the necessary few thou clearances between the two halves of the top slide dovetails. As there taken up under those cutting loads the slide will take a slightly different angle as the end closest to the cutting tool is jammed against the dovetail and the other end pivots in the opposite direction. The same to a lesser amount because the parts are a bit more rigid happens with the taper turning attachment as well. It's also why light finishing cuts are more accurate because the cutting loads and machine deflections are much less. It's also why cutting a male and female taper using the exact same top slide angle still won't perfectly match each other because generally the cutting forces are acting in opposite directions on the top slide as each taper is cut. Using the cutting tool upside down and cutting on the back side of the female taper can help duplicate the same loads as what happened while cutting the male taper. It's simple physics, but not quite as obvious as it would seem because it's happening at levels that can't easily be observed.

Thanks
your post is a great example of what it means to 'think like a machinist'. Its all Mewtonian physics and Euclidean geometry, but understood at a level of precision that is both beyond direct sensing and unfamiliar to 'mere mortals' :) Heck, its hard enough to cut a good 45 deg mitre in a piece of oak. Morse tapers are several orders of magnitude more precise.
A
 
@Anatol: Thank you very much for sharing this! I have seen very little info on use of a taper attachment.

I have a SB 13" lathe with the taper attachment. I have used it one time and it worked nicely, but I still have many questions. I don't have a good understanding of how the taper attachment controls the cross feed in place of the lead-screw. In the video, he removes a screw that should release the lead screw nut, but when I take out a similar screw in my lathe, the nut is still attached. So this mechanism is still mysterious to me. My lathe is a mid-70's machine.
 
@Anatol: Thank you very much for sharing this! I have seen very little info on use of a taper attachment.

I have a SB 13" lathe with the taper attachment. I have used it one time and it worked nicely, but I still have many questions. I don't have a good understanding of how the taper attachment controls the cross feed in place of the lead-screw. In the video, he removes a screw that should release the lead screw nut, but when I take out a similar screw in my lathe, the nut is still attached. So this mechanism is still mysterious to me. My lathe is a mid-70's machine.

I think the video is from way back and might not totally apply to later machines. Mine is a 1941 and I dont have a screw to remove prior to using the TA.
 








 
Back
Top