Misterg
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I got asked about the toolpost spindle that I use in my mini lathe, so I thought I would post some info here. I'll describe it 'as it is' - there are improvements I've yet to make, and changes to the basic design that I'd make if I were to start again.
One of the main limitations of mini lathes is their *very* restricted cross slide travel. My spindle has to be flipped over (which means swapping the motor mount to the opposite side of the body) between cross drilling and face drilling to give a reasonable working envelope.
Set up for cross drilling:
Set up for face drilling:
The original idea was that the body of the spindle would be twice centre height (so that the spindle was on centre which ever way up it was), and the toolpost bolt would fit through it. It dawned on me during making it that the main body of the spindle needs to be well behind the toolpost to allow a reasonable diameter workpiece / length of drill to be accommodated. I made up a 'quick and dirty' mount to test this out, and... that's what I'm still using. One day I'll make up something which is a bit more rigid... One day...
(One day I'll make a cover to stop swarf getting into the motor... One day...)
The heart of it is a 10mm diameter straight shank ER11 collet chuck. The only modification was to drill and tap the tail end of it M4. (The first one I bought didn't run true, but the second one was very good, so worth checking them.)
The whole thing was made on the lathe - the spindle is mounted in a block of 38mm square aluminium bar that was trued up in the 4 jaw chuck - rough and ready cross-section:
The front bearing is a 3200 double row angular contact bearing and the rear bearing is a plain ball bearing. There was originally a spacer sleeve between the two bearings so that they could be clamped up tight with the outer race of the rear bearing floating in the housing. I though that it would be a good, solid bearing, but actually there was quite a bit of axial play in the double row A/C bearing (my fault - I didn't appreciate that this would be the case). To get around this, I just removed the spacer and used the clamping screw in the rear of the spindle to preload one half of the A/C bearing against the rear bearing. One day I will replace both bearings with opposed A/C bearings with a proper preload adjustment... One day...
The 12V / 3000RPM motor came from a child's ride on toy (they stopped crying eventually).
The spindle pulley is 32T and I use either a 20T motor pulley + 200mm belt or a 64T motor pulley with a 252mm belt to gear it up or down from the motor without drastically altering the centre distance. 99.99% of the time I have it geared down, but running at full speed, so ~1800 RPM spindle speed. (Geared up, it only gives me 6000 RPM. I could go higher, but then I would need to change the spindle pulley. I haven't felt the need to use it for grinding - yet... One day...)
On a decent power supply, the motor has huge torque, but on the lathe I just run it from a plug-in 12V brick and a small 5 amp PWM controller. This limits torque a bit when geared up, but doesn't cause any issues when geared down.
I keep meaning to put the controller into a box before I kill it - I've even got a box - but haven't got around to it yet... One day...
When combined with an indexing plate on the chuck of the lathe, it has proved to be incredibly useful for drilling mounting holes, etc. in turned parts and is quite capable of milling and drilling steel.
Timelapse of 5mm HSS end mill in steel:
Could it be designed better? Yes. Is it useful as it is? Heck, yes!
One of the main limitations of mini lathes is their *very* restricted cross slide travel. My spindle has to be flipped over (which means swapping the motor mount to the opposite side of the body) between cross drilling and face drilling to give a reasonable working envelope.
Set up for cross drilling:
Set up for face drilling:
The original idea was that the body of the spindle would be twice centre height (so that the spindle was on centre which ever way up it was), and the toolpost bolt would fit through it. It dawned on me during making it that the main body of the spindle needs to be well behind the toolpost to allow a reasonable diameter workpiece / length of drill to be accommodated. I made up a 'quick and dirty' mount to test this out, and... that's what I'm still using. One day I'll make up something which is a bit more rigid... One day...
(One day I'll make a cover to stop swarf getting into the motor... One day...)
The heart of it is a 10mm diameter straight shank ER11 collet chuck. The only modification was to drill and tap the tail end of it M4. (The first one I bought didn't run true, but the second one was very good, so worth checking them.)
The whole thing was made on the lathe - the spindle is mounted in a block of 38mm square aluminium bar that was trued up in the 4 jaw chuck - rough and ready cross-section:
The front bearing is a 3200 double row angular contact bearing and the rear bearing is a plain ball bearing. There was originally a spacer sleeve between the two bearings so that they could be clamped up tight with the outer race of the rear bearing floating in the housing. I though that it would be a good, solid bearing, but actually there was quite a bit of axial play in the double row A/C bearing (my fault - I didn't appreciate that this would be the case). To get around this, I just removed the spacer and used the clamping screw in the rear of the spindle to preload one half of the A/C bearing against the rear bearing. One day I will replace both bearings with opposed A/C bearings with a proper preload adjustment... One day...
The 12V / 3000RPM motor came from a child's ride on toy (they stopped crying eventually).
The spindle pulley is 32T and I use either a 20T motor pulley + 200mm belt or a 64T motor pulley with a 252mm belt to gear it up or down from the motor without drastically altering the centre distance. 99.99% of the time I have it geared down, but running at full speed, so ~1800 RPM spindle speed. (Geared up, it only gives me 6000 RPM. I could go higher, but then I would need to change the spindle pulley. I haven't felt the need to use it for grinding - yet... One day...)
On a decent power supply, the motor has huge torque, but on the lathe I just run it from a plug-in 12V brick and a small 5 amp PWM controller. This limits torque a bit when geared up, but doesn't cause any issues when geared down.
I keep meaning to put the controller into a box before I kill it - I've even got a box - but haven't got around to it yet... One day...
When combined with an indexing plate on the chuck of the lathe, it has proved to be incredibly useful for drilling mounting holes, etc. in turned parts and is quite capable of milling and drilling steel.
Timelapse of 5mm HSS end mill in steel:
Could it be designed better? Yes. Is it useful as it is? Heck, yes!
