On ideal bench-top mill

[rashid11]

Basic reqs

- sq column
- X travel: 20", Y: 9", Z: 15" , spindle to table: 19", all give or take an inch
- weight: 600 lb
- varaible speed with consistent torque, 0 - 3000 rmp
- CNC conversion-friendly

The clear winner: RF45 square column clones.

There's a quite a number of geared head square column mills: Grizzly, IH,
LM, ENCO, Penntool etc etc. None use DC motor and rely on gears to keep the torque
up @ rather limited set of speeds. I don't think geared head in these serve
any other purpose.

Yet these mills are nearly ideal: just the right weight, size, table size and travels. They are definitely conversion-friendly and are very capable machines, that still would fit into most folks basements/garages etc.

Not only that, when disassembled, no part of it seems to weight more than
200 lb (IH version) - so one can service it easily by himself.

There's a guy that put a DC motor into his Bport: http://www.truetex.com/dcdrv.htm and he loves it. I was wondering if one easily modify the "geared head" model in the same way ? Ideally throw away
40 lb of gears and somehow manage to drive the spindle directly via a Vbelt ?

BTW - the Bport the guy modified - does it drive the spindle's pulley directly ?

[Mcgyver]

if it actually maintains torque then it would work, but the slowest speed on on mine is 100 rpm and there are times i wish it was less, for example using a big fly cutter. If I've a motor spinning at a couple thousand rpm and generating 3 hp, can it actually put out 3 hp at 25rpm? in other words is the torque of the motor linear about a rotation?

[rashid11]

From what I read at the site I mentioned (do read through it, quite
interesting), the torque is quite amazing, down to lowest RPMs. Of
course I was talking about variable-speed DC motor ...




From http://www.truetex.com/dcdrv.htm :



The drive is a joy to operate, with the tiny dial giving complete control of the motor speed from 0 to 1750 rpm. For routine work, I keep the pulley on the third-highest step, disengage the backgear, and use the speed control dial to set the proper speed for the application. By varying the step-pulley and backgear combinations, I can further vary speed and torque with gear ratios in various steps from about 1.6 down to 0.046. Since the motor develops about 3 ft-lb continuous torque (and a potential for some multiples of that), the spindle can be geared down to a few rpm at over 65 ft-lbs, which translates to several tons of force on the edge of a 1/2" cutter. Try that with your VFD!

[wizard]

Originally Posted by rashid11 Basic reqs - sq column - X travel: 20", Y: 9", Z: 15" , spindle to table: 19", all give or take an inch - weight: 600 lb - varaible speed with consistent torque, 0 - 3000 rmp - CNC conversion-friendly The clear winner: RF45 square column clones.

Actually i was giving serious consideration to one of the Mini Knee Mills. But when it comes right down to it the box column mills are probably a better idea for a conversion to a machine that will primarily be used with CNC.

Laugh if you want but the one thing I don't like about the box column mills is that the table sits very low with respect to eye level. A knee mill on the other hand keeps the tool within a specific working envelope.

There's a quite a number of geared head square column mills: Grizzly, IH, LM, ENCO, Penntool etc etc. None use DC motor and rely on gears to keep the torque up @ rather limited set of speeds. I don't think geared head in these serve any other purpose.

Gearing is there so that you have torque available. I do not reccomend brushed DC motors on such machines, you would be better off keeping the gear box and adding an AC drive or brushless DC drive.

If you are flush With $$$ a brushless drive might do the trick.

The big concern I have with these machines is the durabiltiy of the gear train. Haven't really had much in the way of feedback with respect to that.

Yet these mills are nearly ideal: just the right weight, size, table size and travels. They are definitely conversion-friendly and are very capable machines, that still would fit into most folks basements/garages etc. Not only that, when disassembled, no part of it seems to weight more than 200 lb (IH version) - so one can service it easily by himself.

Be careful with that "seems" parts fo those mills might be heavier than first thought. Further they aren't easy to handel. Otherwise yes they are very close to being ideal.

There's a guy that put a DC motor into his Bport: http://www.truetex.com/dcdrv.htm and he loves it. I was wondering if one easily modify the "geared head" model in the same way ? Ideally throw away 40 lb of gears and somehow manage to drive the spindle directly via a Vbelt ? BTW - the Bport the guy modified - does it drive the spindle's pulley directly ?

One thing worth keeping in mind here is that it is worth finding out as much context information as possible about how a machine was converted. Just because a usage is described as being wonderful for one persons usage does not imply that everyone will benefit in the same way.

In other words be careful about jumping into a conversion. Understand what is being done and how it impacts your usage.

Dave

[MikeAber]

rashid11,

Thanks for sharing the info on the bridgeport conversion.

I am also considering the conversion of one of my gearhead mills to the DC motor and controller configuration without the gearset. I think a two speed timing belt drive with speeds selectable from the gearhead via one of the gearchange levers, a 1.5 horsepower 5100 rpm DC motor with 2:1 reduction for low range and 1:1 for high range would be ideal. The spindle bearings in the gearhead mills are marginal at anything over 5,000 rpm.

Mike

[ChrisJ]

I have been considering a future conversion of my IH mill.

Aaron at IH has been tinkering with converting one of his mills to a belt drive. From what I hear he was successful.

My future conversion would be as follows:
1.Remove gears and make it belt drive (1 to 1 ratio).
2. Put a 2HP TENV, 1800 RPM motor (Blackmax or equal). Largest motor (TENV) that will fit without hitting the dovetails on the Z column.
3. Drive the motor from a vectorless drive, or purchase the motor with an encoder and use a vector drive. The combo Duramax drive with a Blackmax motor with encoder is not rudiculiously high on Automationdirect.com.

Theorectically unless I am off base, this configuration gives you constant torque from 0 to 1800RPM. A constant sloped torque line from 1800 to 3600 RPM, where the torque would be about half at 3600 RPM, and a maximum speed of around 5000 to 5200 RPM. Those motors won't overheat at near zero RPM and they have a maximum RPM spec of around the 5200 RPM.

This has been the best solution that I have investigated so far.

Chris