Crossfeed dial bearing extension

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1949DC
Posts: 39
Joined: Thu Apr 02, 2020 6:31 pm

Crossfeed dial bearing extension

Post by 1949DC »

I currently have a 8 tpi and would like to switch over to a 10 tpi. The dial I have is worthless so a new 200 grad dial also. I plan on thrust bearings and new nut etc. My concern is how much bearing extension on the crossfeed crank is too much. Currently I don’t have any issue turning the crossfeed and bed cranks at the same time hitting knuckles. I want some extension so I can use a longer throw on my crank but having the extension too far out would that be awkward leaning in to view work and working both cranks. For those that have improved the size of dials and added extension have you wished the extension to be shorter or even longer?
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Crossfeed dial bearing extension

Post by pete »

No bearing operates well with unbalanced turning forces and long extensions outside the bearing race. Every machine tool out there keeps the handle as close to the sleeve or rolling bearing as possible. Modifying outside those normal parameters will always have increased negatives. While it was done for the top slide to move the operating handle up and away from possible interference issues with both the cross slide hand wheel and tail stocks casting, George Thomas in the UK designed a kit http://www.hemingwaykits.com/acatalog/G ... rd_S7.html to gear the feed screw to the off set operating handle in it's new position. Unless you use a total of three gears then with only two the feed screw and nut then needs to be opposite handed to keep the slide movement in the same direction as the lathe came with. So moving the hand wheel and dial up and to either direction sideways your cross feed could be done in the same way with a bit of thought and still keep the distances short and allow a longer throw crank. One other simpler way would be to build a longer version of what your lathe already has for mounting the bushing or bearing the cross feed feed screw and hand wheel rotates on. If I want to modify anything on machine tools I try and think about why they did things as they have. There's almost always very good engineering reasons for those design choices.
1949DC
Posts: 39
Joined: Thu Apr 02, 2020 6:31 pm

Re: Crossfeed dial bearing extension

Post by 1949DC »

http://www.wswells.com/projects/jim_ben ... e_dial.pdf

Interesting bit of engineering from George Thomas
I’m referring to increasing dial size and working with larger cranks. The compound crank is also too small. For now I want to make the extension for the crossfeed. A needle cage bearing will easily support the feed screw shaft near the crank. One could make the extension very long if properly supported. This is not practical of course but asking what might be a comfortable length.
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