[Stutank]

Hi to all

Having just purchased a mill/drill with a dovetailed column, i have to consider where my Z axis motor should be, on the quill or driving the head up and down on the column. I have seen mills similar to mine where the quill is driven, however the column has some advantages that i can see.

Are there any disadvantages.

[gd.marsh]

I can't think of any disadvantages to driving the entire head. And I can't think of what one would gain by driving just the quill.

You can get away with a less powerful motor & shorter ballscrew on the 'quill only' conversion .. but the cost savings for that would be minimal compared to the over-all cost of a quality conversion.

Also the Chinese mills are rather notorious for sloppy quills that in some cases can move around up to a couple thou in the XY plane. Granted the ways are not exactly of the highest precision either, but at least they can be lapped & the gibs can be adjusted to take up some slop.

[eartaker]

I'm with gd.marsh on this one, drive the head and lock down the quill.

[ramkitty]

driving the quill would be a pita to zero ever time you move the head to change tool or whatever and you loose a lot of rigidity by extending the quill.

[Stutank]

Thank you all for your help. It confirms what I though, but i see so many commercially converted mills with just the quill cnc'd, thought i had missed something (must be cost cutting).
Actually my mill (Like a RF-45) has very little work left to finish it (just optional bits). I drive the head on the column (Quill remains locked), and it is certainly very convienient to be able to move the head up 450mm and out of the way. Can take a mean cut as well, no quill to promote chatter.

[aarggh]

Did you end up going ahead with this, and if so, what rating stepper did you use?

cheers,
Ian

[Stutank]

Yes i did, and all is finished and working now. The performance is good both with the heavy work and the light (but intricate) work.

The motors are Keling dc servo motors (KL34-180-90) via Gecko G320x drivers X, Y driving at 1 : 1 and Z axis at 2.5 : 1, and the ball screws are 20 dia x 5 pitch , cheap chinese ebay type (but very happy so far). I limited the travel speed to 2400 mm/min, and this combination does it easy (so it should).

Other features used are :-
Inverter Drive to the spindle giving up to 3200 rpm.
Central lubrication system for Slides etc.

[SCzEngrgGroup]

Beware: The KL34-180-90 servos have been known to blow-up Geckos if the machine crashes..... Not a problem with the smaller ones.

What kind of mill is this that you feel it needs such large motors? I used the KL-170-90s on my knee mill, and it does 350IPM, and will break a half inch endmill without losing position. I used the same motor to move the 750# knee.

Regards,
Ray L.

[Stutank]

This mill is probably the heavy end of the bench top mill/drills. Overpowered Yes, but does not work up a sweat while working hard in a 40 degree C ambient (other than the spindle motor and gearbox, but not an issue).
The only blowup to date was caused by spindle motor dropping out on motor current, when using a 50mm face mill. This stopped the axis dead (current limit or count error) as it should. I was able to reset and continue at reduced feed.

[mwood3]

Thank you all for your help. It confirms what I though, but i see so many commercially converted mills with just the quill cnc'd, thought i had missed something (must be cost cutting).
Actually my mill (Like a RF-45) has very little work left to finish it (just optional bits). I drive the head on the column (Quill remains locked), and it is certainly very convienient to be able to move the head up 450mm and out of the way. Can take a mean cut as well, no quill to promote chatter.

most of the "low end" commercially prepared Knee mills do drive the quill...its a very simple setup for one piece type job shops...some also CNC the Knee but this is slightly less common...if they need that capability most would just step up to a VMC. Im with the rest on this...on a benchtop CNC if you have the option, CNC the head and keep the quill locked(looks like you did that)

[SCzEngrgGroup]

The primary reason to NOT use the quill is that the fit of the quills on these small machines tend to be pretty sloppy, and will not give you a good result, as the quill will be able to move around quite a bit when extended any reasonable distance. If you'rs is tight, even when extended, then no reason not to use it, except you will not be able to do everything with the quill, and will still need to move the head, for example, when going from a very short endmill to a long drill. On my knee mill, I ran for about a year using the knee as the Z axis, then finally built a quill drive. I now use the quill for all cutting, and use the knee to apply tool length compensation, so I always have full quill travel available for all tools. But, then you're talking talking a 4th drive, motor, etc.

Regards,
Ray L.

[aarggh]

I like the idea of driving the quill, and using the knee for tool comp, but I must admit i'm concerned if there's any long term ramifications to the mill using it in this fashion? Reason I'm so interested in this thread is that i'm getting a mill from Advanced Machinery in Dandenong next year, and was originally looking at a smaller DM45-46/Vario BF16 type of bench mounted one to cnc retrofit, but ended up going for a much larger one (V1000) as the quality seems really good and the cost wasn't that much more, but it's more along the lines of the Hare and Forbes HM50-52 models, very big and heavy. About 700kg. I think it's maybe too big a job to drive the knee for this one, and the cast iron wear concerns me.

I guess if I ensure the knee is always as high as possible to allow for each job, and I minimise the extent of travel of the quill as much as possible, then wear and tear, and exposed forces to the quill would be minimum? Or am I over worrying?

cheers,
Ian

[SCzEngrgGroup]

I like the idea of driving the quill, and using the knee for tool comp, but I must admit i'm concerned if there's any long term ramifications to the mill using it in this fashion? Reason I'm so interested in this thread is that i'm getting a mill from Advanced Machinery in Dandenong next year, and was originally looking at a smaller DM45-46/Vario BF16 type of bench mounted one to cnc retrofit, but ended up going for a much larger one (V1000) as the quality seems really good and the cost wasn't that much more, but it's more along the lines of the Hare and Forbes HM50-52 models, very big and heavy. About 700kg. I think it's maybe too big a job to drive the knee for this one, and the cast iron wear concerns me.

I guess if I ensure the knee is always as high as possible to allow for each job, and I minimise the extent of travel of the quill as much as possible, then wear and tear, and exposed forces to the quill would be minimum? Or am I over worrying?

cheers,
Ian

I don't think I've waste too much time worrying about "cast iron wear", unless you're going to be operating the machine in a volume production environment on an extended basis. Just keep it well lubed and it should be fine. You're correct that you need to be very aware of quill usage if you don't use the knee (or head) to compensate. Keep in mind, too, that Mach3 does not currently provide a built-in means of using the knee (or head) to apply tool compensation - G43/G49 ALWAYS operate on the Z axis, and you CANNOT change that. That is one thing I've asked Brian to change at some point (probably v4). I had to do it through custom macros, and some non-standard G-code.

[Stutank]

My mill conversion is now 4 years old, and it may be of interest how it has gone after doing a fair amount of work.
Basic Mill - (Larger bench top Mill/Drill Dovetail Column) - I would do the same again, an ideal machine for my usage.
Ballscrews - Cheap Chinese (Ebay types) - still going well with no end play. Supplied support bearings / housings all replaced, not up to the job.
Conversion - The large servos and gecko drives - No issues, works well. Certainly overpowered, but no downside to date. (I haven't crashed yet, however)
Wear - Support bearings excepted (Now 2 years on SKF's no Problem) all checks out. I check each axis every 6 months or so, measure backlash / disconnect motors and "Feel" for issues with the slides. Slides, if there is any wear, they have worn in not out. barely touched the gibs.
Quill - Remains locked at all times, I would say that if you have a dovetail column, drive it not the quill.

The only regret that I have is not fitting a 2.2kw VSD to the 1.5kw Spindle motor. The motor is 4 pole 1.5kw. I run up to 100 Hz to give 3000 rpm, and is well capable of the higher power above 1500 rpm. The spindle has cut-out on current limit a couple of times.