[aarongough]

I've been making a lot of threads lately, so what's one more!

I need a 5C spindle for my CNC gang-lathe build, but unfortunately 5C spindles by themselves are kind of hard to come by. I almost got my hands on a great Dunham 50M spindle, but I missed it unfortunately.

I was thinking about building a spindle completely from scratch, but making the spindle body is a little challenging for the equipment and skills that I have. Building the headstock will be difficult, but I think within my reach.

So, I have decided to make a spindle using the guts of a 5C spin indexer.

I bought a spin indexer from LittleMachineShop: Indexing Spin Jig, 5C - LittleMachineShop.com with the intention of evaluating it for the purpose.

After getting the spin indexer I was a little worried at first impression, but after pulling it apart, wiping it down and taking some measurements I am quite reassured. The OD of the indexer spindle varies only 0.0002" between the nose and heel end, it does slope in the wrong direction (larger toward the heel) but I think that can be worked around.

The spindle wall just behind the taper is about 0.125", the spindle wall behind the shoulder is 0.2"

The OD of the spindle body is 1.7715" at the midpoint, 1.7714" behind the shoulder at the nose end and 1.7716" at the heel. This means that 45mm ID bearings should fit it quite nicely.

Next step is to measure up the spindle for CAD and draw up the headstock assembly.

[aarongough]

Ok! I drew up a model of the spindle from the 5C spin indexer in SolidWorks.

The model is dimensionally accurate to about 0.005" in all respects except the spindle taper and some minor irrelevant detail.

I also excluded the threads from the spindle nose as I have no need to model those right now.

I've attached a render of the part, plus a ZIP file containing both an STL and SLDPRT of the spin indexer spindle (from the LittleMachineShop spin indexer in case anyone else is looking for dimensions!)

[aarongough]

Next step is bearing selection.

I've been doing a lot of thinking and research on this topic. The most 'correct' choice would be to use either angular-contact or tapered-roller bearings. Angular contact are favorable for higher spindle speeds and tapered roller are favorable for their higher stiffness due to increased contact area.

I was not able to find any tapered roller bearings that were sealed or even shielded, so that pretty much puts them out of the running. I have no desire to waste space on oil seals or make a labyrinth seal.

Angular contact bearings are an option still, but I've been unable to find any sealed or shielded single-row bearings with a 45mm inner diameter. (If anyone has an online supplier please let me know!)

So the plan, for now, is to do with 6209 series sealed deep-groove ball bearings. Their axial load-carrying capacity is rated at 50% of their radial capacity, which should be more than enough for my small lathe. There are also a lot of angular-contact bearings in the same 45x85x19 size, which means a swap later is easy and feasible if necessary.

I've been trying to decide between going with:
- a pair of bearings at the nose of the spindle and a floating support bearing at the heel
- a single bearing at the nose, and a single bearing at the heel with the preload running between them

Interestingly enough I think that even though the second option *sounds* simpler, it's actually much harder to accomplish as the faces for the two bearing pockets would have to be exactly parallel even though they'd be machined in 2 separate operations.

This makes the first option the likely candidate.

Does anyone have any thoughts on reasons why the headstock shouldn't be made of aluminum? (Barring rigidity... I know it won't be as good as steel or CI, but given the relatively large size of the headstock block I think it should be enough.)

[Bob La Londe]

While, not a perfect answer, you can make into your design the ability to put some load on your deepgroove bearings the same way you might on your anglular contact bearings. Many cheap mills and routers use back to back skate bearings with a spacer in between for this with fair results.

I too have thought of using an indexer as the core of a lathe spindle. I will definitely be following this thread and hoping you succeed in making a great build.

[aarongough]

While, not a perfect answer, you can make into your design the ability to put some load on your deepgroove bearings the same way you might on your anglular contact bearings. Many cheap mills and routers use back to back skate bearings with a spacer in between for this with fair results.

I too have thought of using an indexer as the core of a lathe spindle. I will definitely be following this thread and hoping you succeed in making a great build.

That's pretty much what I had in mind. The bearings will have a spacer between them on the spindle side, and will then be preloaded via a screwed retaining ring on the headstock.

I'm going to draw up the concept later tonight.

Thanks for following along! Hopefully the build will be successful!

[aarongough]

Did a more detailed model of the spindle, just for the hell of it. I'm using the project to learn Solidworks.

[ninefinger]

I've been trying to decide between going with:
- a pair of bearings at the nose of the spindle and a floating support bearing at the heel
- a single bearing at the nose, and a single bearing at the heel with the preload running between them

Interestingly enough I think that even though the second option *sounds* simpler, it's actually much harder to accomplish as the faces for the two bearing pockets would have to be exactly parallel even though they'd be machined in 2 separate operations.

This makes the first option the likely candidate.

Does anyone have any thoughts on reasons why the headstock shouldn't be made of aluminum? (Barring rigidity... I know it won't be as good as steel or CI, but given the relatively large size of the headstock block I think it should be enough.)

IF you go with the widely spaced bearings then aluminum for the headstock would be a bad choice due the difference in thermal expansion between it and the steel spindle. It would really mess with your preload.

I personally don't think a separate oil seal is a wast of space - its a design necessity if your running quality bearings.

Just remember that "tolerance stack up" also applies to the overall stiffness, so using standard deep groove bearings, using aluminum for the headstock, etc will all contribute to lowered rigidity and you may not be happy with the final result.

Mike

[aarongough]

IF you go with the widely spaced bearings then aluminum for the headstock would be a bad choice due the difference in thermal expansion between it and the steel spindle. It would really mess with your preload.

I personally don't think a separate oil seal is a wast of space - its a design necessity if your running quality bearings.

Just remember that "tolerance stack up" also applies to the overall stiffness, so using standard deep groove bearings, using aluminum for the headstock, etc will all contribute to lowered rigidity and you may not be happy with the final result.

Mike

Hey Mike!
Thanks for the input! Your point about rigidity stackup is definitely worth keeping in mind.

I would use oil seals and un-shielded bearings, but I simply don't think there's room with the spindle body that I'm using unfortunately. I'll try a mock up with open angular contact bearing and oil seals.

I agree with you totally about the widely spaced bearings and aluminum, that would be trouble.

Honestly the choice of headstock material is probably going to come down to cost. I think the cost per volume is lower with aluminum, and I'm also familiar with working it.

I'll do some finite element analysis in solidworks and see what the deflections are like with both materials. Will report back.

-Aaron

[Bob La Londe]

I'm not sure about something the size and weight of a lathe spindle, but a lot of small spindles are designed with 2 back to back bearings in the nose that are fixed to the Spindle into the housing, and the bearing in the rear or far end of the spindle is floating. I know a number of high speed Mill spindles are designed that way.

[wizard]

Hey Mike!
Thanks for the input! Your point about rigidity stackup is definitely worth keeping in mind.

I would use oil seals and un-shielded bearings, but I simply don't think there's room with the spindle body that I'm using unfortunately. I'll try a mock up with open angular contact bearing and oil seals.

Even if you use shielded or sealed bearings you should still consider protection for them at the spindle nose. I really don't see space as an issue here, it is really a question of keeping your bearings viable.

I agree with you totally about the widely spaced bearings and aluminum, that would be trouble.

It is a question of design. Beyond that even a castiron housing will expand differently then the spindle shaft. This mainly due to thermal differentials.

Honestly the choice of headstock material is probably going to come down to cost. I think the cost per volume is lower with aluminum, and I'm also familiar with working it.

For this approach cheap makes sense. You should consider casting your own housing.

I'll do some finite element analysis in solidworks and see what the deflections are like with both materials. Will report back.

-Aaron

Keep in mind heat gain and disapation will be different.

[Skyfire]

Next step is bearing selection.

- a single bearing at the nose, and a single bearing at the heel with the preload running between them

This way will work too. but only one single bearing on each end is not enough rigidity. And the the hard point is what you mentioned of the machining on both end to be parallel in 2 steps. Another issue is that may have problem of grinding in and preload adjustment.

I did have some successful appliactions this way on a spindle. using a pair of angular bearing of DT(back to face) type on each end, and adjust preload carefully then. The spindle can run upto 6000RPM and 0.0002" error with P4 class bearings. It runs pretty smooth without thermal rising problem and accuracy loss. So should be some successful project.

So I suggest two pairs of angular contact bearings of at least P5 class on both end if go this way.

[mactec54]

aarongough

You don't want to waste you time with the oil seal, make a labyrinth seal, they are easy to make, oil/grease seals for a lathe spindle get messed up with little use, If you are doing light duty, you can use the deep groove Bearings, this is what Emco uses on there small lathes, they work ok but are not the best idea, Most likely the best for what you want to do will be the Taper roller bearing, the cheapest as well, ( 1 ) at each end is all you will need, you set the preload with a spacer in the middle/between the 2 bearings

[aarongough]

I'm not sure about something the size and weight of a lathe spindle, but a lot of small spindles are designed with 2 back to back bearings in the nose that are fixed to the Spindle into the housing, and the bearing in the rear or far end of the spindle is floating. I know a number of high speed Mill spindles are designed that way.

Good point. I've seen a number of spindle designs with the dual bearings at the nose, but they've all been smaller spindles. I'll make a point of having a look at the service manuals for some larger lathes this weekend and see how their spindles are setup.

Probably best just to copy!

[aarongough]

Even if you use shielded or sealed bearings you should still consider protection for them at the spindle nose. I really don't see space as an issue here, it is really a question of keeping your bearings viable.

Good point! I'll work on fitting in secondary shielding at the spindle nose.

It is a question of design. Beyond that even a castiron housing will expand differently then the spindle shaft. This mainly due to thermal differentials.

For this approach cheap makes sense. You should consider casting your own housing.


Keep in mind heat gain and disapation will be different.

I would love to make a casting! Learning to make cast pieces is definitely on my list, but I think it will have to wait until after this project unfortunately.

[aarongough]

This way will work too. but only one single bearing on each end is not enough rigidity. And the the hard point is what you mentioned of the machining on both end to be parallel in 2 steps. Another issue is that may have problem of grinding in and preload adjustment.

I did have some successful appliactions this way on a spindle. using a pair of angular bearing of DT(back to face) type on each end, and adjust preload carefully then. The spindle can run upto 6000RPM and 0.0002" error with P4 class bearings. It runs pretty smooth without thermal rising problem and accuracy loss. So should be some successful project.

So I suggest two pairs of angular contact bearings of at least P5 class on both end if go this way.

Interesting point about the single vs double bearings. I guess that is the same sort of thinking as for ballscrews with 'supported' vs 'fixed' end fixity.

I can get double row angular contact bearings without much trouble, so that's definitely an option. The main question is whether I'll run out of space.

[aarongough]

aarongough

You don't want to waste you time with the oil seal, make a labyrinth seal, they are easy to make, oil/grease seals for a lathe spindle get messed up with little use, If you are doing light duty, you can use the deep groove Bearings, this is what Emco uses on there small lathes, they work ok but are not the best idea, Most likely the best for what you want to do will be the Taper roller bearing, the cheapest as well, ( 1 ) at each end is all you will need, you set the preload with a spacer in the middle/between the 2 bearings

Good to know that oil seals are too fragile.

I know what a labyrinth seal is, but I've never seen the anyone go through the process of making one, and I don't know how large the individual 'teeth' should be.

Any resources you can point me to?

[Skyfire]

Interesting point about the single vs double bearings. I guess that is the same sort of thinking as for ballscrews with 'supported' vs 'fixed' end fixity.

I can get double row angular contact bearings without much trouble, so that's definitely an option. The main question is whether I'll run out of space.

Yes. pretty much as you said. just like the "fixed" end for ballscrews.

I guess one single tapered roller bearing on each end will work too considering strongger than angular contact ones. But safe MAX speed I guess should around 3000-4000RPM because the MAX RPM of ID45mm tapered roller bearing should be around 6000. Just a guess.

BTW. In the benchtop building thread in this forum, I will use the angular contact bearings for the spindle the same way as I did. I think it can reach MAX 6000-8000RPM with P5/P4 class bearings. I think it will work well too. but the initial target of this spindle is 3000RPM now. I will see then.

Cheers~

[Bob La Londe]

Are dual row ACBs going to give you the reduced play in the spindle of a properly setup back to back pair of single rows?

Why would size be an issue. You are building from scratch after all. Build it whatever size you need for the design you decide on.

[aarongough]

Are dual row ACBs going to give you the reduced play in the spindle of a properly setup back to back pair of single rows?

Why would size be an issue. You are building from scratch after all. Build it whatever size you need for the design you decide on.

Size is an issue because the spindle from the 5C indexer that I'm using is only 6" long... The double-row bearings are about 1.5" long each, so it's easy to start running out of room.

I had a look around for some diagrams of large lathe spindles. I could only find ones from manual machines, but they all seem to use pairs of tapered roller bearings separated by the length of the spindle.

I'm not sure how using double-row bearings would affect stiffness. I assume that double row is better than single row, but I'm sure there could be some cold hard fact that I'm missing in there.

[mactec54]

aarongough

My post here may give you a idea of how to make one, this is a smaller diameter than what you want, but you can make it just larger to suit your spindle

http://www.cnczone.com/forums/cnc_wo...dle_build.html