PM-30MV with BT30 Spindle?

[gmoschini]

I have a PM-30MV on order, and I'm considering possibly upgrading the headstock/spindle assembly from R8 to BT30.

The thought is to replace the spindle with a Chinese BT30 belt-driven spindle to get 6000/8000/10000 RPM, and combine it with a 1.5kw/2.2kw AC servo spindle.


The headstock would be replaced with an assembly made of 3/4" steel plates and 3/4" wall steel tube, with 1" steel plate for the back plate to attach to the Z axis dovetail block.

And eventually, to add one of these BT30 ATC assemblies.













Would this kind of spindle and motor be too much for the PM-30MV?

Keep in mind, it already has a 3000 RPM spindle and a 1.5KW brushless motor.

Sanity check requested.

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[cncuser1]

As far as spindle power goes, it depends on what you will be cutting, although more power is always nice, more weight on the head isn't. Especially with your spindle adapter idea.
Your plan to build-up the spindle has too many risks: rigidity, cracked welds and warping over time.

If you must build it up rather than start with a solid block, then the shape you came up with is springy in the +/- X direction, the box needs to be closed in the front and the round tube needs to protrude though the top and bottom plate in order to get proper welds. The entire assembly should be normalized before machining to size. But in the end don't weld it up.

The BT30 and the rest of the machine can work very hard, your spindle idea will by far be the weakest part of the machine..

[gmoschini]

As far as spindle power goes, it depends on what you will be cutting, although more power is always nice, more weight on the head isn't. Especially with your spindle adapter idea.
Your plan to build-up the spindle has too many risks: rigidity, cracked welds and warping over time.

If you must build it up rather than start with a solid block, then the shape you came up with is springy in the +/- X direction, the box needs to be closed in the front and the round tube needs to protrude though the top and bottom plate in order to get proper welds. The entire assembly should be normalized before machining to size. But in the end don't weld it up.

The BT30 and the rest of the machine can work very hard, your spindle idea will by far be the weakest part of the machine..

Welding 3/4" and 1" plate is probably out of the question, I don't have a welder (yet).

I was originally thinking that the plates would be mechanically joined, bolted together steel plates.

I could also do the same with cast iron plates, bolted together.

However, as you mentioned machining the entire head out of a block of gray cast iron is also a possibility.

The cast iron head would still need to be bolted to the Z block.


Plans for cutting would be mostly aluminum, hence the desired higher speeds.

[pippin88]

Probably better to buy a mill with a 30 taper spindle

[gmoschini]

Probably better to buy a mill with a 30 taper spindle

Probably, yes.

But if I could have done that, I probably already would have.


Yes, the Tormach 1100 MX comes with a BT30 spindle.. but $20k is way outside of my price range.


In any case, I'm going to explore the idea of building a head stock out of a block of cast iron.


If I can get a block of G2 or 65-45-12 Dura-bar cast iron about 6"x6" x 10" long I'm sure I could mill it out.

OnlineMetals lists 6.03x6.03 milled bar, but it's $1100 for a 6-foot piece.

They say you can request a quote for a shorter cut, a 1 foot piece would probably do.


https://www.onlinemetals.com/en/buy/...-bar/pid/24200

[gd.marsh]

Not quite sure how the PM-30 compares to the ZX45 in physical size, but I was able to purchase a BT30 spindle to replace the stock R8 spindle that came in my Bolton ZX45 machine.
I have a somewhat older (& lengthy) thread in the 'RF45 Clone Mill' section of the zone .. Look for 'Bolton ZX45 Conversion'.
It's towards the very end of my thread where the BT30 spindle went into my machine. Very happy with that change!

gd.marsh

[gmoschini]

The ZX45 style is comparable to the PM-932M in that it has the same RF45-based frame:

https://www.precisionmatthews.com/shop/pm-932m/


However it's about $800 more than the PM-30MV which I have on order:
https://www.precisionmatthews.com/shop/pm-30mv/


It IS a much heavier machine, though.

And the bed / travels are slightly smaller.


Do you think it's worth upgrading to the PM-932M for the heavier weight?

[arizonavideo]

The PM-30 is just large enough for 56C size motor.

A 2HP with a larger pulley can get you 6 or 8K with good power. The 30 is not that large so 6K with a 1/2 cutter is about right.

You would need to change to AC bearings. The R8 could be re ground to CAT 30 fairly easy.

[DEVILHUNTER]

I'm on a similar project. I have a WMD30 (similar size than yours) with full rail conversion. The weakest point of your mill is going to be the column, I wouldn't spend that much money until you reinforce that column as best as you can.

After my rail conversion I spected less chatter, but noticed that increased a lot. Now I have bolted the whole column to the cinder block wall and it has got better, but still I'm thinking on filling the block with concrete.

Anyways, once I actually get the column reinforced enough, the weakest point of my mill is going to be the spindle (MT3 with TTS). The whole headstock is also not that stiff, I think, So my idea is replace the headstock and use the same spindle cartridge. Maybe even modify it to get through spindle coolant...

[gmoschini]

I'm going to call PM this morning and ask about upgrading to the PM-45/PM-932 instead.

It'll have the slower RPM geared head, but I think the stronger frame would be a better base to upgrade it from.

[gmoschini]

I'm going to call PM this morning and ask about upgrading to the PM-45/PM-932 instead.

It'll have the slower RPM geared head, but I think the stronger frame would be a better base to upgrade it from.

The order is updated! Will ship by the end of November due to the PM-1030V lathe being on backorder.


For $1010 extra, I upgraded from a PM-30MV to a PM-932M, with the Power Down Feed and Cast Iron stand options.

I also added a 2nd 5" vise and ultra-precision collet set.


I'll have to think about the options for converting its spindle to 1:1 belt drive with servo spindle, and changing the spindle to BT30.


ArizonaVideo, you mentioned regrinding the spindle to BT30?

I'd imagine I'd have to get a tool-post grinder to do that... would I do that directly on the mill?

Or take the spindle out and grind it on a lathe with a 4-jaw chuck?


I would probably also need to grind slots in the end for the BT30 driving pins... and drill and tap the ends.

Maybe when the time comes I'll just buy a spare spindle from PM and make the changes on that.

[gmoschini]

On further review, I am glad I decided on the RF-45/PM-45/PM-932m.

Charter Oaks Automation has a NT30 spindle that's a replacement.

eBay also has a ton of NT30 spindles for Bridgeport heads that may also match - at least the bearing diameters are the same, not sure about the length.

[gmoschini]

Further exploring the idea of a PM-932m with a 90mm diameter Chinese BT30 spindle mounted in a giant block of cast iron.

Making the block tall gives it contact surface area with the Z saddle, and the large slot in the top provides a belt path between the servo and the spindle, 2.2kw AC servo as a stand-in.


Material cost ballpark on a 7.68" x 9.18" x 12" long block of 65-45-12 cast iron is roughly $300 from OnlineMetals, and comes in at a whopping 220 pounds.

Good thing though, the PM-932m would be beefy enough to mill its own replacement head, especially if I convert it to CNC first.


Lastly, I must thank KCJ for posting the excellent models of the RF-45 mill, they've helped tremendously.

I live in Atlanta, maybe when the time comes I can enlist the help of someone to modify the frame parts with the necessary clearance cuts for CNC.

[gmoschini]

Looking at this AC Spindle Servo as an example:

SZGH08-3-9.5-1.5/2.2-4-1500
https://www.szghauto.com/product/91.html

150x150x345mm outline for the motor, weighs 25kg/60lb.

9.5 N.m torque, or 1345 oz-in, flat line torque from 4000 rpm to 6000 rpm, max RPM 8000.

Up to 3x torque at low speeds for rigid tapping/cutting.


I found a BT30 Chinese spindle rated for 10,000 RPM, 12000 RPM max


2.2kw AC servos are the same, but taller and a bit heavier.

[cncuser1]

7.68" x 9.18" x 12" long block of 65-45-12 cast iron is roughly $300 from OnlineMetals, and comes in at a whopping 220 pounds.

sommething looks off there, 220 pounds seems high for that size.

[gmoschini]

sommething looks off there, 220 pounds seems high for that size.

It's what the web site said, 220 pounds per linear foot of that material, at those dimensions.

Cost is estimated to be around $300 for 1 foot, not including shipping.

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[gmoschini]

Further updates will be in this build thread:

https://www.cnczone.com/forums/rf-45...2-cnc-cad.html

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