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Tool Trek #2: Rockwell 28-3x0 Bandsaw w/3 phase motor

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Blog entry by magaoitin posted 07-03-2017 04:34 PM 1018 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 1: Powermatic 60 8” Joiner Part 2 of Tool Trek series Part 3: The Search for Unifence »

The next auction purchase I made was a Rockwell 28-3X0 20” wood and nonferrous metal bandsaw.




The X stands for X-Treme…no, no it doesn’t. I have read that the X series was specifically sold to government agencies, school districts, and technical colleges. And obviously that applies to this saw. There are stickers for a local School District and a Technical college.





Nearly every auction I have purchased a major tool from in the last 18 months has been done sight unseen through online auctions (the only exception being my Oliver tablesaw, that was at a live auction). Most of the sites I watch have a couple of photos and a brief description, and always say to come and inspect, but my work schedule makes that impractical.


publicsurplus

This is one of my favorite auction site, and I would encourage you to check it out and see what is being offered in your state (unless you live in Washington State, then disregard this, it is a horrible website and you will be endlessly disappointed, hopefully that sounds sincere). It reps State and local municipality equipment along with a number of school districts and technical colleges, nothing is private or commercial.


I go into these thinking that the equipment is used pretty hard, but usually maintained fairly well. It’s either students learning how to use equipment for the first time, or it’s been in a State/Government carpentry shop and is usually very well maintained… For the most part, I have come to the conclusion that a lot of this equipment isn’t broken in any way, but it has reach a point in the accounting world that it needs to be replaced with a new piece. This seems to be especially the case with State owned equipment. The equipment runs great and is serviced regularly, it’s just older.


There were about a dozen photos and this description for the auction.

http://www.publicsurplus.com/sms/all,wa/auction/view?auc=1766064

Not sure how long they cache the webpage but here is the description:

Band Saw, Rockwell, 28-340, 220V, 3 PH, Untested

MAKE : Rockwell

MODEL : 28-340

DESCRIPTION:

Up for auction is a Rockwell Delta Band Saw in unknown condition. Unit could not be tested due to incompatible plug.

Dolly is not included in auction.

No additional accessories included in auction.

Auction only includes the item as described and any other machine/equipment seen on pictures in the surroundings are not part of this auction.

Item is sold “as is” and we strongly recommend the bidders to self-inspect the auction item.

We have forklifts and personnel onsite to assist with load out if needed.

Please see the pictures and the shipping info below for details.

WEIGHT : 698 lbs. w/ Plt

DIMENSION : 80”H x 32”W x 42”D – Lot Size

OVERALL CONDITION : Used

COMPLETENESS : Unknown

SELLING : “As is”


This auction site usually does a great job of including a photo of the motor nameplate, and I read 3 phase 2 hp.



As soon as I had won the bandsaw (and before I had picked it up), I purchased the TECO FM50 2 HP VFD from FactoryMation. For a single phase input and 3 phase output for $167.
TECO FM50 AC Drive, 2 HP, 230V 1 / 3 PH Input, 230V 3 PH Output, 7.5FLA, IP20

I have seen a number of threads on phase conversion for 3 phase equipment on LJ’s and the consensus seems to be split (50-50) on just replacing a 3 phase motor with a single phase and save all the headache of a converter. But then you have the headache of making sure the motor frames are the same bolt pattern along with getting the RPM’s close to the same, changing out the pulley, removing all the electronics for the thermal overload and contactors (I think you can use the contactors from a 3 phase motor on a single phase motor but not really sure). I decided that $175 for a VFD was better than $500+ for a new single phase motor and less hassle.


This post is not for the real electricians on this forum, as you guys already know and understand 3 phase power, but more from the point of view of someone like me just learning about electric motors (and 3 phase power.) Prior to my Joiner purchase, I had never bothered with the details of 3 phase power, other than what was needed for my job. As a general contractor working on industrial and commercial projects, I manage electrical subs installing 3 phase on regular and medium voltage up to 15kVa all the time.


That being said I have never personally wired a 3 phase plug or messed around with an electric motor, I hire other people to do that. 120V/240V I know and understand fairly well and wired 99% of my shop by myself (I didn’t make the final 3’ connection from the meter base to the panel, but that had more to do with my limited time before an inspection).





I got the saw home, offloaded it and finally looked at the plug and my heart missed a beat.

They also included a photo of the plug in the auction photos, which I conveniently ignored.


What I “missed” in all of this is that while the description for the auction said 220V, it is actually wired for 480V (it’s right there on the plug Jeffrey!) and a phase converter will do nothing to Step-up the voltage. I had spent $400 on the saw and $167 on the VFD and was sure I had just wasted nearly $600, plus taking a day off work to drive down to pick up the saw.



The motor nameplate lists that this is a multi-voltage, 208V, 220V, and 440V motor and it looks like a fairly new motor (for some reason the manufacture date isn’t put on nameplates…) Since I didn’t know anything about 3 phase motors (and was unaware at the time) you can change the Voltage of some motors with some very simple wiring. Still it was something I have never attempted.

Great, sounds simple, that is what youtube and a fire extinguisher are for right?…I got lucky and in this case it was just that simple. I still have my eyebrows, and the fire department got to take the afternoon off. It took me longer to get the motor out than it did to rewire it.
When I took the motor out, some kind mechanic had written on the motor that it was replaced in ’98, so it’s a new-ish motor.





I opened up the cover on the motor, and all of the wires were labeled, so it was as simple as hooking up the wires in the order on the schematic. For low power, in my case 240v
1 + 7 + the L1 on the power cord
2 + 8 + L2
3 + 9 +L3
and 4, 5, & 6 together



Next step was to wire the motor up to the VFD and make sure it wasn’t fried or the bearings had gone in it. Per the VFD manufacturer you are supposed to wire the motor directly to the VFD, bypassing the ON/OFF switch, the conductors, thermal overload, and motor starter components. The VFD controls everything. You can also wire the ON/OFF switch directly to the VFD, along with a speed control, which I plan on doing in the future, along with mounting the VFD inside of the saw somehow.





The bench test went great so I put the motor back in the saw, and everything seems to work. For the electricians out there, disregard the white wire in the photo, I will hit it with a black sharpie when I do the final mounting)




I thought as an added bonus (until I dedicate the VFD to this machine) I would wire the VFD to a wall mounted receptacle and will be able to plug in any piece of 220V 3 phase equipment (2 HP and under). This was handy when I was tinkering with my Powermatic 60 motor, before attempting the Static Phase Converter idea.


So for just under $600 I have a 20” variable speed wood and metal band saw that is running on single phase power, and has a VFD so I can theoretically dial the speed down even further and cut steel. Unfortunately, reality is getting in the way of me cutting steel.

The Fallacy (for me at least) of cutting ferrous steel with a VFD on a Wood Bandsaw.


I was going to create a simple speed chart to hang next to the saw for metal conversions, but once I ran the numbers I still shouldn’t be cutting steel with this machine.

The VFD reads off from hertz so at 60 hz it is at full power, 45 hz is 3/4, 30 hz is 1/2, and so on. While I have 2 pulleys on the machine for high speed (wood) and low speed (non ferrous metal) it is a colossal pain to change the belt. I have it set on the lower (smallest driver pulley and smallest driven pulley) speed. I doubt I will ever need the high speed for wood.




With the VFD at full power (60 hz) I am running 4850 sfpm

My motor is 1760 rpm
The pulley on the motor (driver pulley) is 5”
The driven pulley is 9.5” (my larger pulley is 12”)
And the bandsaw wheel diameter is 20”



Motor RPM X motor pulley diameter divided by driven pulley diameter X band wheel diameter X 3.1416 divided by 12 = SFPM


If I have done my calculations correctly at 50% power (30 hz) I’m 2425 sfpm
And at 25% power (15 hz) I should be running 1200 sfpm

So I am running about 81 sfpm per hz.

I haven’t tried cutting anything under 10 hz yet, but theoretically at 5 hz I’m down to 405 sfpm
Which is still way too fast for cutting steel, any lower and the motor slows to a halt.

I did not like the way I wired the VFD and mounted it to the wall. I have been looking for an inexpensive NEMA enclosure, and have even though about making a small cabinet to house the VFD, but so far haven’t found anything I like.




The one positive aspect of how I had set things up was I had a 20A 240v 3 phase receptacle in the shop I could plug anything into,

The drawback to this setup with the VFD on the wall, is I cannot easily wire the ON/OFF switch on the Bandsaw back to the VFD, and I don’t want more loose wires strung from a piece of equipment. I also did not like the idea of surface mounting the VFD to the Saw, as I would have the same basic issue of loose wires, and this time with no way to install a cabinet that would not have been a giant eyesore.

I thought about removing the motor control box on the back of the machine and mounting the VFD there, but I am reluctant to remove and throw out the 3 phase starter/controller. I suppose if I got the ON/OFF switch wired to the VFD and a potentiometer wired in, I could mount the VFD on the back of the saw. But I have another idea.

-- Jeff ~ Tacoma Wa.



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