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spindle bearing fitment and retention

TorontoBuilder

TorontoBuilder

Sapientia et Doctrina Stabilitas
I sort of know how to design a spindle using traditional deep groove ball bearings set in a bearing pocket, and retained by a bearing cap, with a bearing spacer or boss to fix the axial location of the spindle within the housing as shown below.

The pulley end of the spindle would be the similar except there would be a belleville washer between a pulley and the bearing spacer. A nut tightens the pulley and provides a preload onto the bearing via the washer.

This design can handle the speed, radial load and moderate axial load involved with light external grinding.

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My query is regarding spindle design for high speed precision grinding of internal features on parts. I wish to use a bearing with greater precision and speed capabilities, so I sourced a needle roller bearing which are press fit, and require lubrication but that bear on the ground and hardened spindle shaft itself (or separate race) and therefore lack an inner race to abut the bearing spacer. This leaves me with the quandary of how to axially fix the position of the spindle within the housing.

I'd like to use such bearings for their precision and their high speed capabilities so I am looking for ideas on how to how to affix the shaft in the housing bore to prevent lateral movement of the shaft.

All I can think of is perhaps using delrin or teflon washers, or thrust bearings in place of bearing spacers. My worry is the lower precision of thrust washers could affect the spindle run out, and that all these options limit the spindle speed. My target is 16000 to 18000 rpm even though the bearings are capable of much higher speeds.

Can press fit alone prevent axial movement of the shaft?




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From the reading I've done, they are inevitably angular contact on the business end so the preload is taken care of. And the other end is a bearing that is allowed to slide with thermal expansion. That's usually where the springs or Bellville washers are. Now there are spindles that have 2 or more roller bearings (or tapered bearings in high axial load) on a shaft and a mechanism to set them into or apart from one another to take up play. But I have only seen those on light duty and/or less precision and/or manageable heat which is a big deal. I wish there was a good, step by step spindle cookbook but I haven't seen one. So much relies on the bearing selction themselves. I think what most guys do is copy or scale something that works, but that presumes you have the information readily available. If you look at how a Dumore or Themac or similar functions, they pretty much set the bar. And that might only be 1/4-1/3 HP driving it.
 
You have to set the shaft so the business end can't move relative to the housing, have it take radial and axial loads as well as having something movement as the shaft warms up

There are some light, decent spindles that use deep group ball bearings or even magneto bearings. All that I've seen create a preload with spring or stack of belleville washers.

Better still, why not just use back to back angular contact bearings and retain both the inner and outer race with nuts? The one's I've done, I did that on the business end then allowed the other to float in the bore with a deep groove bearing.

With the quality now of universally matched, you don't have to spend a fortune. You have to buying NSK or SKF or something quality, but when do their universally matched ones are really good ...... and not too expensive compared to matched. That does away with the need to grind spacers to set the preload.

I've designed and built a few precision spindles (P4 bearings), probably the most demanding work I've done. You have to be able to grind to tenths to meet the fit requirements of the high precision bearings or you wreck them.
 
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I'll add that I desire the OD of the bearing housing to be 32mm which makes the spindle be under 18mm between 15mm - 18mm to be more precise.

I'll have a look at angular contact bearings to see what can be found as @Mcgyver suggests
 
Just to prove I am not as Stubborn about YouTube as some might think. I am in bed with a cold/flu here. So I decided to watch a few RRenzetti videos. Saw this one on making a precision spindle. Thought you might like it.

 
Mcgyver said:
Better still, why not just use back to back angular contact bearings and retain both the inner and outer race with nuts? The one's I've done, I did that on the business end then allowed the other to float in the bore with a deep groove bearing.

With the quality now of universally matched, you don't have to spend a fortune. You have to buying NSK or SKF or something quality, but when do their universally matched ones are really good ...... and not too expensive compared to matched. That does away with the need to grind spacers to set the preload.

I've designed and built a few precision spindles (P4 bearings), probably the most demanding work I've done. You have to be able to grind to tenths to meet the fit requirements of the high precision bearings or you wreck them.
Click to expand...

If you ever care to share a sketch, coffee stained napkins with ballpoint scribbles... I'd love to have a look. Now if I need a grinder to make a spindle to grind then I should probably pass anyways LOL

Quite a while back I bought a book: Spindles by Harprit Sandhu - workshop practice series #27. I pull it down once in a while & then put it back again. Its hobbyist orientated which is fine if generic layouts is all you are after. But its very light on technical details - what is to be supported, how big or small is enough, what floats & by how much.... I can kind of trace how loads are being transmitted & compensated but that's a far cry from understanding. Maybe there are engineering text books on the subject but that's kind of the issue - a rather wide informational gap in between basic & high end.

Clough published his TPG spindle which looks generically like others including the Sandhu book. OK, in the final episode it spins & he made a surface shiny before moving onto another project so I really don't even know how it compares in the grand scheme.

I'd like to see what's inside a (was it a Deckel?) spindle head Stefan adopted to his tool post in a very early video. Its these small compact ones I'm most interested in. And I keep wondering if these ER shafts couldn't somehow be adapted. The one I got for my TCG Franken-spindexer seems decently high quality, at least compared to what I could make. I should stop, I'm imposing on Toronto's thread

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Susquatch said:
Just to prove I am not as Stubborn about YouTube as some might think. I am in bed with a cold/flu here. So I decided to watch a few RRenzetti videos. Saw this one on making a precision spindle. Thought you might like it.

Click to expand...
Thnks I've watched it a few dozen times, always learn more with every viewing, but not helpful to this specific application
 
PeterT said:
If you ever care to share a sketch, coffee stained napkins with ballpoint scribbles... I'd love to have a look. Now if I need a grinder to make a spindle to grind then I should probably pass anyways LOL

Quite a while back I bought a book: Spindles by Harprit Sandhu - workshop practice series #27. I pull it down once in a while & then put it back again. Its hobbyist orientated which is fine if generic layouts is all you are after. But its very light on technical details - what is to be supported, how big or small is enough, what floats & by how much.... I can kind of trace how loads are being transmitted & compensated but that's a far cry from understanding. Maybe there are engineering text books on the subject but that's kind of the issue - a rather wide informational gap in between basic & high end.

Clough published his TPG spindle which looks generically like others including the Sandhu book. OK, in the final episode it spins & he made a surface shiny before moving onto another project so I really don't even know how it compares in the grand scheme.

I'd like to see what's inside a (was it a Deckel?) spindle head Stefan adopted to his tool post in a very early video. Its these small compact ones I'm most interested in. And I keep wondering if these ER shafts couldn't somehow be adapted. The one I got for my TCG Franken-spindexer seems decently high quality, at least compared to what I could make. I should stop, I'm imposing on Toronto's thread

View attachment 56196View attachment 56197
Click to expand...
dude, impose away.

I share your interest in the subject. Luckily I have a grinder and a machinist experienced on it to grind things for me. But I want for my shop not my brothers. The small spindles are what I desire, and I've thought why not use pre-made spindles. but I see a few issues based on their hardness and ability to machine easily.
 
PeterT said:
Quite a while back I bought a book: Spindles by Harprit Sandhu - workshop practice series #27. I pull it down once in a while & then put it back again. Its hobbyist orientated which is fine if generic layouts is all you are after. But its very light on technical details - what is to be supported, how big or small is enough, what floats & by how much.... I can kind of trace how loads are being transmitted & compensated but that's a far cry from understanding. Maybe there are engineering text books on the subject but that's kind of the issue - a rather wide informational gap in between basic & high end.

Clough published his TPG spindle which looks generically like others including the Sandhu book. OK, in the final episode it spins & he made a surface shiny before moving onto another project so I really don't even know how it compares in the grand scheme.


View attachment 56196
Click to expand...

I have both those resources by the way, and I find them light on technical information, but harpit did give me some ideas. You just never know what will spark the imagination. Like this photo above. My bias at looking at all my current spindles and typical online ones and I'd never have thought to put the pulley on the same side of the spindle housing as the grinding wheel.
 
Susquatch said:
Just to prove I am not as Stubborn about YouTube as some might think. I am in bed with a cold/flu here. So I decided to watch a few RRenzetti videos. Saw this one on making a precision spindle. Thought you might like it.

Click to expand...
Don't click on this link, there is no doubt that Sus has been hacked and some Nigerian prince is attempting to drain your bank account.
 
The needle roller bearing will not provide any reliable axial fixation and will be destroyed if you try. I think its been mentioned but the most practical design for a grinder spindle is similar to a lathe/mill spindle but scaled down. 2 angular contact bearings back to back near the business end take all the axial and radial loads from the grinding work, and a single deep groove bearing out back takes the radial load from your belt and pulley and can float axially.
Having the 2 angular contact bearings in close proximity to one another helps mitigate bearing tightening/loosening with changes in temperature, and having them near the working end also helps in this regard, as the spindle changes length with temperature the total change from the point of fixation (bearing) and the working end is reduced.

Now at 45000 or 50000 rpm (like that GMN spindle) that introduces other worries - resonance and balance which can change your bearing strategy. Those can also be a concern at 16 to 18K but if the spindle is small enough maybe not balance as much, and keeping the spindle as short as possible helps.
 
Mike R said:
The needle roller bearing will not provide any reliable axial fixation and will be destroyed if you try. I think its been mentioned but the most practical design for a grinder spindle is similar to a lathe/mill spindle but scaled down. 2 angular contact bearings back to back near the business end take all the axial and radial loads from the grinding work, and a single deep groove bearing out back takes the radial load from your belt and pulley and can float axially.
Having the 2 angular contact bearings in close proximity to one another helps mitigate bearing tightening/loosening with changes in temperature, and having them near the working end also helps in this regard, as the spindle changes length with temperature the total change from the point of fixation (bearing) and the working end is reduced.

Now at 45000 or 50000 rpm (like that GMN spindle) that introduces other worries - resonance and balance which can change your bearing strategy. Those can also be a concern at 16 to 18K but if the spindle is small enough maybe not balance as much, and keeping the spindle as short as possible helps.
Click to expand...
Great points to consider too, and mesh well with Mcgyvers. I have a much better idea of the method to proceed. Now I just need to sort thru all the options on skg's website
 
To be honest, now that I have a mill with one of the ER20 spindles that does 10K to 24k rpm, I'm looking at it and thinking it could be mounted on the lathe and be a great grinder....
Easy, fast, and relatively cheap - wat more do you want?
 
Mike R said:
To be honest, now that I have a mill with one of the ER20 spindles that does 10K to 24k rpm, I'm looking at it and thinking it could be mounted on the lathe and be a great grinder....
Easy, fast, and relatively cheap - wat more do you want?
Click to expand...
Well the ability to fit into a tool holder wud be sweet...
 
Mike R said:
To be honest, now that I have a mill with one of the ER20 spindles that does 10K to 24k rpm, I'm looking at it and thinking it could be mounted on the lathe and be a great grinder....
Click to expand...

thinking out loud, great on the mill but how would it be grinding i.e. what is the vibration level? Reason I ask is I've a dumore and wolf TPG, and while both are good, they are not great. Vibration levels produce a an ok but not great ground finish compared to what you'd expect on a cylindrical grinder. So I'm thinking if a decent quality TPG are just ok, what's the finish going to be like for an even rougher set up (or maybe its as smooth or better a set up?

I even tried dynamically balancing (home made setup) the motors.

Last time did this (ID only, I do the OD's a T&CG with a motorized work head) I used an internal grinding spindle from a Cincinnati T&CG and it was better. A far more substantial spindle than on the TPGs and everything including the mounting block is cast iron. Motor is isolated a bit by 1/2" sheet of rubber. I use a Consew motor which was both quite low cost and was very smooth; a marvellous combination. Still, its a battle to great results and its a lathe so tenths accuracy is rather elusive. It's not like adding a TPG fully addresses grinding, imo. Still a comprise. Ultimately, a cylindrical grinder is the right tool for the job.....oh for more space.


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Mcgyver said:
I do the OD's a T&CG with a motorized work head).
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I'll be doing the same for short lengths on surface grinder.

In hopes of getting the best possible result I purchased an ID OEM spindle

Mcgyver said:
Still a comprise. Ultimately, a cylindrical grinder is the right tool for the job.....oh for more space.
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The lament of hobby machinists everywhere. If I had space I'd be all over a nice smaller cylindrical grinder. I even know one in perfect shape with little use that should be for sale soon
 
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