# Square Column Mill Belt Drive Questions



## TomS (Nov 6, 2016)

I searched this forum and a few others on square column mill (ZX45, RF45, PM932, etc.) spindle belt drive conversions but didn't find the specific info I was looking for.  Hopefully you all can answer my questions.


First question - why are most conversions ending up with a top speed of around 6,000 rpm?  AC and deep groove bearings speed ratings are around 9,000 to 10,000 rpm depending on method of lubrication (oil or grease).

Second question - what are the recommended high and low Hz operating parameters?  I've seen numbers as high as 140 Hz but not a lot of information as to why.

Third question - how low of a Hz setting can you run at and still have ample torque with large end mills or face mills?  

Fourth question - why two step pulleys, why not three step?  Wouldn't that give you a wider rpm range with a narrower Hz band?  

TIA,

Tom S.


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## jbolt (Nov 6, 2016)

You held out on speed longer than I thought you would. 

First question - why are most conversions ending up with a top speed of around 6,000 rpm?  AC and deep groove bearings speed ratings are around 9,000 to 10,000 rpm depending on method of lubrication (oil or grease).

I'm using an import 2hp 3ph inverter rated motor and Huanyang VFD. The recommendations I got were to keep it under 100hz. I run up to 105Hz with no issues. This gets me to 6K on the spindle in high gear (2:1). A high quality motor can be run above 120Hz. 6K has been fast enough as most of my milling is done with 1/4" to 1/2" end sized mills. I rarely use the low gear (1:2) unless I am doing steel or using a drill bit over 5/8". There ws a guy on the CNC zone that did a PM-45 conversion and was running 8K with a marathon motor. If I recall he started out with inexpensive AC bearing which he fried and then went to high end AC bearings. I went middle of the road on cost/quality.


Second question - what are the recommended high and low Hz operating parameters?  I've seen numbers as high as 140 Hz but not a lot of information as to why.

My VFD is programmed at 20Hz to 105Hz. Most ops are done at 60Hz and above but I will go as low as 30Hz for some ops. A better motor and VFD would provide an wider Hz and torque range.


Third question - how low of a Hz setting can you run at and still have ample torque with large end mills or face mills? 

In high gear (2:1) I can run my 4" 45deg face mill at 2k (35Hz) with a max 0.1" DOC in aluminum. For large end mills I run up to 3/4" in aluminum. For example a 3/4" 2 flute HHS end mill at a DOC of 0.5" will run at 2500 rpm (44Hz) and 15 IPM. My jobs in steel typically run 1500 RPM or lower so I switch to low gear. If it is a small job in steel and I do not want to mess with switching to low I will run the part in high with lighter cuts. Anything below 1k in steel in high cutters will start to stall.


Fourth question - why two step pulleys, why not three step?  Wouldn't that give you a wider rpm range with a narrower Hz band? 

Most of the belt conversions I have seen used an 8-groove poly-v belt (what I did). The usable height of the spindle (and still have a power/pneumatic  drawbar) limits the number of pulleys to two.


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## TomS (Nov 6, 2016)

jbolt said:


> You held out on speed longer than I thought you would.
> 
> First question - why are most conversions ending up with a top speed of around 6,000 rpm?  AC and deep groove bearings speed ratings are around 9,000 to 10,000 rpm depending on method of lubrication (oil or grease).
> 
> ...



Jay - thanks for the info.  I read your conversion thread several times for the purpose of putting together a baseline.  Now with the additional information you just gave me I can start to put a plan together.  I need to retain quill travel for my tool changer.  It takes about 1" of travel to release the tool holder.  So your answer about three step pulleys helps a lot.

I do have an auxiliary spindle for high RPM machining but I'm limited to 1/4" cutters if I want to do any serious work.  Anything bigger I have to reduce RPM and feed rate otherwise the cutter dances across the work rather than cuts.  

What's getting me going in the belt drive direction is I've been dealing with a local motor repair shop for a contactor for my lathe.  We got on the subject of motors and VFD's and the owner mentioned he had a new 2 HP Teco VFD sitting on the shelf.  One of his customers ordered it several months ago, paid for it, but never picked it up.  He offered it to me for practically nothing if I bought the 3 phase motor from him.  Package price is about $400-$450 including programming the VFD and doing the necessary wiring.  I supply the materials.  Thought that was a fair price. 

Another question.  What is the frame size for the originally supplied PM-932 motor?  Below is a picture of the motor data plate.  Best I can determine it's a frame size 90L.

Tom S.


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## jbolt (Nov 6, 2016)

I have no idea what size frame the original motor was. If that picture is off your motor then yes it is a 90L. That seems to be a typical size for the Asian 2hp motors. The frame size really does not matter since you will need to make a motor mount for the conversion anyway. The motor I have now is a 56C/TEFC.


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## TomS (Nov 7, 2016)

jbolt said:


> I have no idea what size frame the original motor was. If that picture is off your motor then yes it is a 90L. That seems to be a typical size for the Asian 2hp motors. The frame size really does not matter since you will need to make a motor mount for the conversion anyway. The motor I have now is a 56C/TEFC.



Ah yes!  Once I read your comment it hit me that the belt drive conversion mounts the motor above the top of the mill head.  

Tom S.


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## TomS (Nov 9, 2016)

Well it doesn't look like the local electric motor shop is going to work out.  We had a miscommunication.  He thought we were talking about my lathe and I was talking about my mill.  The equipment he has (1 HP rated VFD and motor) will not work.  But the search continues.  I'll scour eBay and Amazon for motors and VFD's and see what I come up with.

Tom S.


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## jbolt (Nov 9, 2016)

Bummer

FYI,

This is the motor I am using. https://www.amazon.com/gp/product/B007IVS1FA/ref=oh_aui_detailpage_o08_s00?ie=UTF8&psc=1

and this is the VFD. http://www.ebay.com/itm/VARIABLE-FR...064113?hash=item3cc836acb1:g:9QEAAOSwLVZVsPgr

So far so good. The Haunyang VFDs seem to be better quality than a few years ago but as anything from China YMMV. The Huanyang VFDs need to be overrated hence the 2.2kw (3hp) unit for a 2hp motor.


If I were to do it again I would consider this VFD. I have the 2.2kw version on my lathe, very nice unit. http://www.ebay.com/itm/HITACHI-WJ2...733300?hash=item2118e75034:g:1nUAAOSw6n5XtJx2

Watch ebay for deals on motors. http://www.ebay.com/itm/2-HP-Motor-...021770?hash=item2cb00a3c0a:g:AZYAAOSwiylXCC0r


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## TomS (Nov 9, 2016)

jbolt said:


> Bummer
> 
> FYI,
> 
> ...



Thanks for the links.  Just started looking at the drives available on eBay.  I've seen a lot of the Hitachi WJ200 mentioned on this forum.  Teco and Hitachi are priced about the same.  Hitachi also has a NES1-015SB that is about $100 less.   http://www.ebay.com/itm/Hitachi-Ltd...523793?hash=item2362356cd1:g:hU8AAOSweuxWT55L.  Any opinions on this one?

Tom S.


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## jbolt (Nov 10, 2016)

I'm not familiar with that one. You might look up mksj on this forum and ask him. He is the resident VFD guru.


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