retro fit of 1100 RPM motor to table saw
johnnyd
| Posted in Power Tools and Machinery on
The motor on my 25+ year old Craftsman contractor saw gave up the ghost, and I got a nice big 1 1/2 horse (Baldor?) saw rated motor on permanent loan from BIL. But it runs at 1100 RPM versus the 3450 of the old motor. Seems simple enough to add a 6″ – 7.5″ pulley to the new motor, and after mounting the motor, it looks to me like there will be plenty of clearance, and the shafts line up right.
I will be re-wiring the cord sets with 12 AWG, and putting in a 30 amp switch so I’ll have plenty of overhead for the 19 amps load of the new motor.
Has anyone done this? Are there any potential clearance issues? Any advice on choosing a new pulley/belt combo?
Replies
There is a possible clearance problem, the path of the belt will be wider and the belt may rub against the underside of the table with the blade raised to its highest position, and the same problem may occur when the blade is at a low position, the belt may rub against the frame of the saw.
Another potential problem is the weight of the motor, if it is heavier than the original motor, may make it even harder to keep the saw in alignment.
John White, Shop Manager, Fine Woodworking Magazine
This gets me thinking maybe I could mock up the pulley with a string to check for potential clearance problems.
I think I'll try that before sinking too much more time or $'s into this.
Also if the motor is longer, it may stick up above the table surface when it is tilted to 45º. Otherwise, go for it.
That motor will probably weigh about twice what the equivalent 1.5 hp 3600 rpm motor would. Size and weight are driven by torque mostly, and the rated torque of that motor (6.9 lb-ft) is almost as much as the torque of a 5 hp motor at 3450 rpm. Could be problematic when tilting the arbor. You may also need to reduce the belt tension a bit, since the motor is so heavy.
Be seeing you...
Well, I fit the motor on yesterday and mocked up a 6" pulley. I think it will line up fine with the arbor pulley, and I verified belt to housing clearances at all positions...raised and lowered, tilted to 45°, etc, and it looks like it was designed to handle a 6" pulley. No issues at all with tilting and lowering functions...especially after I lubricated all the racks and adjustment threads.
Only thing I'm still concerned about is the increased weight and whether or not the whole (trunion?) assembly will stand up to it long term. Also, just checking things out, the arbor bearing is a little noisy but I couldn't detect any end or side play and it certainly turns freely without any binding.
This saw, by the way, has worked through 1000s of board feet of hardwood over the years with nary a complaint until now.
I get the pulley tomorrow...any reccomendations as to type of pulley and belt, and should I also consider upgrading the stock 2 1/2" arbor pulley?
A 6" diameter motor sheave driving a 2-1/2" arbor sheave will only give you about 2800 rpm blade speed, but the torque at the arbor will be nearly 50% more than it would be with the same hp motor and a 4000 rpm blade speed, assuming you don't get belt slip on the small arbor sheave. I don't think you'd have to worry about bogging the blade.
You'd need an 8-3/4" motor sheave to get 4000 rpm at the blade, or 7-1/2" to get 3450 blade speed, with the 2-1/2" arbor sheave you have now. I'd suggest you look into a cast iron motor sheave, since die-cast sheaves don't run all that true. At the larger diameter and higher speeds, and with a motor supported by the belt, that runout will manifest itself in shaking and vibration. Surplus Center has a large variety of finished bore CI sheaves in stock, so you should be able to find what you need for relatively cheap. You can also look in Grainger and McMaster-Carr.
If you use a notched raw-edged A-section belt, you can also use a smaller arbor sheave, which will bring the blade speed up. A practical limit would be about 2.1" PD (pitch diameter). Always use PD and not OD when calculating speeds, especially with small sheaves, or sheaves that are grooved for more than one size belt. Be seeing you...
So then a general question, IF I use a 6" motor sheave, and end up with 2800 rpm, will that be sufficient speed to get an acceptable cut? Most of the work I'm doing now requires glue line rips (no joiner and no plans for one) in 15/16" white oak, which I have been able to do just fine with this saw/fence/diablo 24 tooth rip setup, the old motor, and arbor speed of 3450 rpm.
So I guess the real question now is how much does blade speed really have to do with cutting, within this 2800 - 3450 rpm range? I would think that with adequete torque and acceptable blade speed, I would actually be better off with high torque low speed, as I could then use a more deliberate feed rate with less burning. This is NOT, after all, production work.
A 7 1/2 " sheave may well also clearance ok, I'll try that tonite, but is it really worth the bother if 2800 rpm will be adequete?
Also, since I'll have to buy a new belt anyway, maybe a cog toothed belt with a slightly smaller cast iron arbor sheave (yelding higher rpm) is the way to go... besides the OE sheave that's on there now does look like runs out a bit. I have a motor/industrial supplier that will work with me to get the combination right.
I'm not able to give you any insight into blade speed vs cut quality, so I'll leave that to someone who knows. I don't expect glue-line rips from my saw and have never even given it any thought since I always joint the edge after cutting.
But if you want to change out the arbor sheave too, then you could use a combo like a Browning AK22 (2.2" OD, 2.0" PD with A-belt) and Browning AL64-SP (5.93" OD, 5.78" PD), which will give you 3300 rpm full-load speed and 3400 rpm no-load (speeds are rounded a bit).
If you want to run the blade faster, you could bump the motor sheave up to AL74-SP (6.93" OD, 6.78" PD), giving you 3860 rpm full-load and about 4000 no-load. Another manufacturer may have one with a pitch diameter (for an A-belt) in between those two.
Use a good quality, domestic raw-edge cogged (or notched) belt, from Gates, Browning, Goodyear, etc. Raw-edge belts are, IMO, more precisely made, being sliced from wide belt stock. Wrapped-edge belts seem to have more variation in width, and even small variations will cause noticeable vibrations. I prefer notched belts to link or power-twist belts, but that's just me - too much noise for my taste.Be seeing you...
Thanks, TKanzler, exactly the information I need to take the deer in the headlight stare out when I go back to the supplier tomorrow.
Well, I got a 6.5"cast iron sheave, raw edge cogged belt, and used the OEM 2.5 arbor sheave and it works just fine. I can tell the rpms are less, but once I start pushing wood through and get the motor under load, there is NO drop in rpm and a smooth stready feed yields a nice smooth cut with no messing around.
Only one thing bothers me...on start up and at running speed there is little or no increased vibration, but after switching the motor off and during the final few seconds of run down, there are several heavy vibrations that shake the whole saw.
Seems to be connected to the belt tension...less if the belt is looser, more if it's tighter. Also this is a capacitor start/capacitor run motor, and the vibration seems to occur right after the little "click" (run capacitor shutting off?) you hear as the motor comes to a stop.
Is this normal or do I have some balance/tension/mounting problems?
TIA.
You mentioned in your original post that the motor is a Baldor. Every single-phase Baldor I've messed with (including 3600, 1800, and 1200 rpm motors like yours) goes into regeneration when the centrifugal start switch closes on shutdown. The start and run windings are 'fighting' each other once the start winding circuit is closed. What you're experiencing is normal.
If you want that to stop, and if you have a magnetic motor control (or triple-pole switch), then you can run one of the start winding leads through the unused pole to break the start winding continuity when the switch is off. Delta even made a motor control specifically to do just that at one time, possibly because they were using motors made by Baldor at one time (60's era).
If you're a David Marks fan, you can hear his Unisaw do that on shutdown if you listen carefully. I would imagine most PM66's do that, too, since they all use Baldor motors.Be seeing you...
No, I just wired in a 20 amp light switch.
Will this vibration do any damage ultimately? Maybe I should look into a real switch. Already had to change the location of this one because it was too easy to turn it on by unintentionally pressing my leg against the switch while leaning over to change the blade etc.
If it were me, I wouldn't sweat it unless the motor is bouncing violently on shutdown. I'd be more concerned about an overly tight drive belt from using such a heavy motor, unless you've taken steps to keep the tension reasonable.
You can get an inexpensive mag starter from Grizzly and a few other places. They have recessed start buttons, and a mushroom head or otherwise prominant stop button. I'd unplug it to make blade changes anyway, though.
http://www.grizzly.com/catalog/2006/Main/214Be seeing you...
Large pully=A small pully=B
A rpm=C
B rpm=D
A:B as D:Cand check out Link Belt at Lee Valley. It works very well. I would send a link(no pun intended, but I'll take it), but I haven't figured that out yet.Skidoo
Edited 12/12/2006 1:04 pm by skidoo
Would it still do this if wired for 220?
You know, that's a good question. Configured for 120V, the two run windings and the start winding are wired in parallel. But configured for 240V, the start winding is only in parallel with one run winding, the other run winding being in series with that pair (and therefore out of the loop). It would seem the effect could be reduced. Or not.
I have a couple of Baldors sitting around unused (one 1800, one 1200 rpm), so I'll wire them up for 240V and give them both a try tonight. I'll let you know what I find. I suspect no real difference, but we'll see.Be seeing you...
Well, I wired a cord into the two Baldor motors I have laying around (one 1200 rpm, the other 1800), configured them for 240V, and ran them. No difference in how they stop when configured for 120V - they both regenerate and slow rapidly when the centrifugal switch comes back in, regardless of voltage.
I then lifted one of the start leads from the mains conductor (after starting the motor), then unplugged the motor, and as expected, it stopped smoothly and without the abrupt change in deceleration when the centrifugal switch closed.
So if you want it to stop more gradually, you need to bring out one of the start winding leads to a 3-pole relay or starter, along with the two line conductors. If you want a sketch, I think I may have one I did for another gentleman who didn't want his PM66 to stop the way it did.Be seeing you...
Yes, I believe the shake is going to cause harm down the road, as this is, after all, just a tuned up 25+ year old Craftsman contractors saw, not designed for that much motor hanging out there.
I do need a diagram of some sort, as I have no instruction manual etc to go by. How do I know which ones are the start winding leads? There is a diagram on there re 120 or 220, and instruction sfor reversing the rotation, (the leads ARE numbered) but that's all I have.
Thanks very much for your help on this, TKanzler!
Edited 12/15/2006 7:37 am ET by johnnyd
The start winding leads are numbers 5 and 8. When you reverse rotation, all you're doing is changing the polarity of the start winding with respect to the run windings. Single-phase motors (ones without run capacitors) will run in either direction once they're given a shove, so the start winding is what gives them the shove in the desired direction.
Older small Baldors had brass tags crimped onto the leads with numbers stamped into them, and more current versions have colored leads with the numbers printed. But even if the numbering or color scheme is different, the start winding is easy to find if the motor can be reversed (not all can).
I'll look around for that schematic.Be seeing you...
OK...the leads in there are colored with numbers, and those are the ones..#5&8...that I changed when I reversed rotation.
So...I could get a three-way 20 amp light switch and run another 12 AWG conductor along side the current cable that in effect jumpers one (which one doesn't matter, right?) such that the starter windings are disabled once the swith is "OFF", but energizes them as soon as the switch is "ON"?
By the way this IS a capacitor run motor.
What is that centrifigal switch for, anyway? Just to eliminate the need for a 3 pole switch?
Edited 12/15/2006 9:19 am ET by johnnyd
Capacitor-start (and some other types) use a separate start winding that's not in the circuit when the motor is at operating speed. The centrifugal switch opens the start winding circuit when the motor approaches speed, and closes when it slows (on shut-down). That's what you hear clicking as it slows. On a capacitor-start motor, if the circuit did not open, that winding would burn out if left in the circuit.
Capacitor-start/capacitor-run (also called dual-value capacitor) motors leave the start winding in the circuit all the time, with a run capacitor in series, but they also have a start capacitor to increase the phase shift of the current to better suit the lower start-up portion of the speed range. The centrifugal switch only cuts out that capacitor, not the run capacitor.
This should be the connection diagram for your motor (I think you said 1.5 hp 1200 rpm Baldor)
https://www.baldorvip.com/VIP/drawings/CD0055.pdf?doknr=CD0055&dokvr=00&filename=CD0055.pdf
You can't use a 3-way switch. You need a 3-pole manual or magnetic motor starter, rated for the amperage and hp (at single-phase). It will be a 3-phase starter, but you'll only use two poles for switching the motor, and the third for disabling the start/run winding (marked "B phase" on Baldor's drawing).
I'd suggest you test this out before looking for a new control. You'll need to disconnect either 5 or 8 after you shut the motor off, but before the centrifugal switch kicks back in. It would be best to do that on a bench, without a load connected, and with one of those two leads brought out on a pigtail so you don't have to touch the main winding leads.
You also really shouldn't use a loose piece of insulated conductor - you need a 4-wire cord from the motor to the control.Be seeing you...
Thanks for all your help, TKanzler...great details to know.
Interesting conclusion to this...had a Christmas party Saturday and had about 5 BILs and FIL all look at the new motor installation. These guys for the most part have all at least grown up around machinery of one kind or another, two are still mechanics and two have also worked (one still does) at production-style wood shops.
Upon close inspection, the vibration that had been bugging me was not only present at shut-down, but also while the blade was being driven both on and off load. It almost looked like the 6.5" motor sheave had three flat spots on it.
Various solutions were offered and tried, and after several analysis sessions throughout the afternoon and evening, the one BIL who still does production maintenance at a window factory did some fine adjustment of the belt tension.
Turns out that with too much motor for the saw and the 3X RPM increase from motor to arbor, enough inaccuracies were introduced to create various vibrations that ultimately would have shaken the whole unit to death. The solution is to run the belt loose enough so that it drives the blade under load, but doesn't introduce the vibrations.
So now, when you measure the static belt tension it seems way too loose, but still does fine ripping 15/16" white oak. Smoother start up, very little vibration under load and allows the motor to spin down without fighting. So I can't rely on motor weight to set the tension any more, and need to be a little more finicky about re-setting the tension after blade height changes, but this should work just fine for occasional use.
A compromise, I know, but one that seems workable so far.
It sounds like you might benefit by using a flexible "link belt" rather than a solid "V" belt.
Rich
It is a cogged belt, which is why I think I can get away with such light tension.
Johnny, I had a similar problem with a Craftsman, where I installed a Two horse motor. To reduce the extra weight on the belt,(and pulleys)
I added counter springs attached to a turnbuckle,on the motor mount platform, to relieve the drag and subsequent 'bounce' Once the equilibrium was achieved when adjusting the turnbuckle,the saw worked fine. Occasionally, (when the blade was at maximum height) I would need to add tension with the turnbuckle. Steinmetz.
Here's another interesting update. After the belt tension was identified as the culprit, (see previous post) operation of the table saw continued as normal with ripping, cross cutting, trimming veneer plywood, etc, with continued correspondence of increased vibration with increased belt tension.
Then, quite suddenly, upon start up, the belt flew off, leaving the motor and blade spinning freely. After waiting quite awhile for the blade to spin down and then trying to re-fit the belt, I noticed a large chunk had broken off the arbor sheave.
While I was removing the broken sheave, I managed to break another chunk off the rim. Luckily, I still had the original 2" sheave from the OEM 3450 motor and pressed that on as the new arbor sheave.
What do you know, the whole set-up now operates with much less vibration, no shake during spin down, and very satisfactory results.
My guess is the OEM arbor sheave had already been worn thin from years of service and slipping and finally let go...with the new more powerful motor and cogged belt being the last straws. Furthermore, the beginning stages of arbor sheave failure were probably becoming evident and may have even contributed to the failure of the OEM motor.
Well, live and learn...probably not a bad idea to replace both sheaves as part of any major saw tune-up.
Edited 1/4/2007 9:12 am ET by johnnyd
J D, For the arbor,get a 'machine made' (Cast iron)sheave(pulley) of the size needed . Google up McMaster- Carr.
For the motor, get an adjustable 'Steel' pulley
of/in the range needed.
That pulley works by screwing the two halves closer or wider apart
(for fine tuning the speed ratio) Steinmetz.Edited 1/4/2007 12:50 pm ET by SteinmetzEdited 1/4/2007 12:52 pm ET by Steinmetz
Edited 1/4/2007 12:56 pm ET by Steinmetz
Is the 1100rpm the same horse power as the old one? If so , and if you want the saw to run at the same revs as before there will be a mechanical disadvantage as the pulley on the new motor would have to be aproximately three times the diameter of the one on the saw-more power use especially on start up and it may not have enough grunt.
No, this new one is rated 1 1/2 hp at 1100 rpm...I think it weighs more like 3X the 1hp/3450.
I read most of the replies to your post.Great responses.
If you choose to replace the (usually) small arbor pulley,be aware that the belt around that smaller diameter sheave will have diminished gripping power.
Also, the v belt may deform earlier. A proper v belt works like a wedge in a wedge, so, when the belt deforms, (Wears)it 'bottom's out'
and thereby slips. It has been my understanding, that the engineering of the original pulley size was the most practicable compromise to allow clearance to prevent the belt's/pulley's rubbing the underside of the top when the blade is raised to it's highest point. Steinmetz.
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