Author Topic: Logan Lathe Spindle Mod  (Read 4069 times)

Offline cfellows

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Logan Lathe Spindle Mod
« on: June 21, 2018, 10:26:36 PM »
I have a 1952 Logan model 920 lathe with an 11.5" swing.  It has a single, 50mm x 80mm Ball bearing race on the chuck side of the spindle and a smaller ball bearing race on the back.  A preload is applied to the bearings through the use of two belleville spring washers on the back end.  I think I've figured out how to convert the lathe to spring loaded tapered roller bearings, 50mm x 80mm.  The changes will not be radical and I will be able to convert it back at any time.  I just want to see if the tapered roller bearings will provide better support for the spindle.  I'll post some pictures when the new bearings arrive.

Chuck
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Offline RMO

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Re: Logan Lathe Spindle Mod
« Reply #1 on: June 21, 2018, 11:30:12 PM »
Looking forward to what you learn on this one.

Mike

Offline Ridjobradi

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Re: Logan Lathe Spindle Mod
« Reply #2 on: June 22, 2018, 12:10:32 AM »
Following and looking forward to it.

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Offline cfellows

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Re: Logan Lathe Spindle Mod
« Reply #3 on: June 23, 2018, 01:21:53 AM »
Haven't gotten my new bearings yet, but thought I'd put up a couple of preliminary videos.  This first video is a general overview of the lathe with some mention of what I plan to do.

<a href="https://www.youtube.com/watch?v=m3X-te1t1Bg" target="_blank">http://www.youtube.com/watch?v=m3X-te1t1Bg</a>
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Offline cfellows

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Re: Logan Lathe Spindle Mod
« Reply #4 on: June 23, 2018, 01:34:26 AM »
Here's part 2 of the video series.  In this video, I remove the front plate from the head stock exposing the ball bearing race.  There's also a better description of how I plan to modify the head stock to use the new roller bearing.

<a href="https://www.youtube.com/watch?v=Gy3mCG-ejWk" target="_blank">http://www.youtube.com/watch?v=Gy3mCG-ejWk</a>

I did measure the casting and unfortunately, the back of the casting isn't parallel with the front.  It's about .035" thicker at the base of the bearing bore than at the top.  I was planning to use a long end mill and face off the back of the casting to be parallel with the front, but now I am considering using shims under the back capture ring to make it parallel.
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Offline cfellows

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Re: Logan Lathe Spindle Mod
« Reply #5 on: June 23, 2018, 04:59:32 AM »
To bolt a ring or flange to the back face of the front side of the casting, I needed some threaded holes.  Fortunately, the head stock had 4, 5/16-18 holes drilled most of the way through to fasten on the bearing cover plate.  To avoid removing the head stock from the lathe, I simply extended these the rest of the way through which was only about 0.2" and finished threading them 5/16-18.





I've calculated that I'll need an 80mm OD x .650" spacer ring to fit inside the back of the bore and press against the back of the outer race on the tapered roller bearing.  The new tapered roller bearing is going to require some special considerations for lubrication.  I'll probably pack them in grease to start with and figure out some kind of shield to keep swarf and metal dust out.
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Offline cfellows

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Re: Logan Lathe Spindle Mod
« Reply #6 on: June 23, 2018, 10:22:09 PM »
I removed the spindle today so i could get more accurate measurements.  As I thought, the bore housing the main spindle bearing is a consistent 80mm diameter all the way through.



An interesting thought occurred to me.  The bearing bore is long enough that I could install two 50mm x 80mm ball races end to end and preload them against each other.  Anybody have any thoughts on which is better, a single tapered roller bearing or two ball races.  In either case the front bearing or bearing set would use the standard loading provided by the belleville washers on the other end of the spindle.  One advantage of the dual ball races is that I wouldn't have to worry about lubrication since both are sealed.

Update:

I just measured the length of the bearing bore and I could comfortably fit two tapered roller bearings end to end.  Seems like this might be the best of all possible options???
Chuck
« Last Edit: June 23, 2018, 11:07:15 PM by cfellows »
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Offline cfellows

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Re: Logan Lathe Spindle Mod
« Reply #7 on: June 24, 2018, 10:01:44 PM »
I hope I don't sound like I know what I'm doing here, because it's all kind of a crap shoot.  I'm depending on serendipity more than sound enineering principles.   :-\   I've decided on another, cleaner approach to this problem.  First of all, I am only going to use one tapered roller bearing.  And, instead of attaching a clamping ring to the back of the front casting wall, I've made a steel ring to a snug, sliding fit inside the spindle bearing bore.



The ring is 3.150" OD and the radial wall thickness is about 7/16".  The axial thickness is .535".  I would have liked something closer to .65", but didn't have any stock on hand to make it from and the ring I wound up using was in my scrap bin and very close to the final dimensions.  Not sure what kind of steel it is, but it is really tough and strongly magnetic.  The 3 holes in the face of the ring were already there so I had to work around them.  I drilled 6 radial holes and tapped them 1/4-20.  Once positioned inside the bore, I'll use set screws tightened against the bore of the bearing housing.  I'm hoping this will be secure enough to withstand tension from the pre-load washers and axial force from turning.  If not, I'll go ahead and add clips with adjustable screws to the back of the casting.
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Offline zeeprogrammer

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Re: Logan Lathe Spindle Mod
« Reply #8 on: June 25, 2018, 01:29:08 AM »
I hope I don't sound like I know what I'm doing here, because it's all kind of a crap shoot.

I'm following along. You certainly know more than I do.
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Offline Mike R

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Re: Logan Lathe Spindle Mod
« Reply #9 on: June 25, 2018, 02:40:20 AM »
Chuck,  2 tapered roller bearings back to back will be an improvement over the single deep groove ball bearing that is in there now.  The 2 tapered roller bearings will act to stiffen up the spindle shaft which should help a lot with reducing chatter.  The 2 bearings can be pre-loaded to each other and the whole spindle pre-loaded to the back as it currently is (no change back there at all).

Mike

Offline MJM460

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Re: Logan Lathe Spindle Mod
« Reply #10 on: June 25, 2018, 06:45:15 AM »
Hi Chuck, I am quite interested in your reasoning behind the spindle modifications, it is an interesting challenge.  Fitting two tapered roller bearings back to back would give great radial load carrying capacity for a heavy chuck and workpiece and belt loads, and also provide the necessary axial position and axial load capability, leaving only radial loads on the outer end bearing to resist the overhang moments and accommodate any thermal expansion.  But if they don't fit, did you consider angular contact bearings, again back to back? 

I guess the load carrying capacity either way is more than adequate, so the more important issue becomes accuracy and consistency of spindle location, but that part is a step beyond me. 

MJM460

PS - I wrote this this morning, but Mike had posted before I was able to upload.  But I think we are looking at different aspects of the same idea.
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Offline cfellows

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Re: Logan Lathe Spindle Mod
« Reply #11 on: June 25, 2018, 07:04:42 AM »
I agree that 2 tapered roller bearings back to back would be better, but it's also considerably more complicated to implement.  The single tapered bearing is easy to try with virtually no modifications to the lathe and I'll do that first.  However, I did order two of the tapered roller bearings and they should arrive tomorrow (Monday).  I'm anxious to see what I can do.

Chuck
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Offline cfellows

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Re: Logan Lathe Spindle Mod
« Reply #12 on: June 26, 2018, 02:15:21 AM »
I got the new tapered roller bearing installed.  Turns out two bearings are a non starter since the bearing journal on the spindle is only one bearing wide.  I packed it with wheel bearing grease and the spindle is not as free spinning as before but there is no binding.  Gone try it out for a few weeks and see how it goes.

Chuck
So many projects, so little time...

 

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