# DoAll 16" ML band saw speed indicator install



## BGHansen

This will take a couple of posts because as usual I'll go into nauseating detail. . .  Back story is I bought a circa 1948 DoAll ML band saw between Christmas and New Years last year.  Being 70+ years old, there were a few things that needed some repairs.  DoAll saws are known for their rotating Job Selector wheel which gives recommendations for filing, blade speeds, blade width and blade teeth per inch depending on the material/thickness being cut.  For speeds, the important factor is “feet per minute”.

My saw came with the standard automotive-type speedometer with graduations in feet per minute. I knew the speedo wasn’t working when I bought the saw, I could see the needle in the bottom of the gauge. I finally got around to looking it over, I believe someone had it apart before and lost the steel disk used to magnetically couple the input shaft and the needle shaft. It’s not a serviceable part from DoAll though I could buy a replacement speedo for $1000!


Stock speedo needle shaft was broken




Hman (John Herrmann) had a brilliant suggestion of replacing the original speedo with a Hall-effect tachometer. They’re under $20 delivered off eBay; read out from 10-9999 RPM’s. John’s suggestion, since my saw is a 16” saw, was to put 4 magnets on the wheel so the readout would see 4 “blips” per revolution instead of the normal 1. The blade circumference is 16” x pi (3.14159) or about 50.25”. Dividing the circumference by 4 (for 4 magnets) gives a spacing of ~12.6” between the magnets. Sure, 12” would yield a readout of exact feet per minute, but I’ll live with the 5% error.


Digital tach for <$20 off eBay.  Uses a Hall-effect pickup and magnet.




I started by making a mounting plate for the tachometer. Material was 16-gauge galvanized sheet metal. I rough band sawed it to size and punched a 3/8” hole through the center. A 3/8” bolt was used as an arbor and the disk was turned round on the lathe.


Dykem'd the 16-gauge stock and rough cut to shape



3/8" bolt for an arbor, pecked away on the lathe to clean up the edge




The disk was Dykem’d and the mounting hole for the tachometer was scribed on the blank. Now, how to cut out the hole? I have a Roper Whitney #218 punch press and could have gone that route, but instead used the DoAll. My saw has a blade welder, cut a 10’ length of ¼” x 32 tpi blade, fed it through the center hole in the blank and welded the blade. I rough cut the hole, split the blade at the weld and used a die filer to finish the hole. I used the RW #218 and a 5/16” punch to knock in 4 mounting holes.


Feed the blade through the center hole with TEETH DOWN so the scribed pattern was on top



Welded, annealed, ground and re-annealed the blade



Ready to knock out the center hole



Last cut



Filing to fit



Punching in four 5/16" mounting holes




Next was mounting the magnets to the back side of the wheel. The Hall-effect tach’s work with a magnet. The sensor “sees” the magnet go by its tip, does some math, and indicates RPM’s. My plan (thanks again John!) was to mount 4 magnets so instead or reading RPM’s, it’s reading increments of 12.6” or very close to feet per minute.


Sharpie marked the magnet locations.  Used a caliper to mark the distance from the edge of the wheel though I suspect the Hall-effect sensor tolerance is pretty big.  The instructions said the magnet should be between 1mm - 10mm from the sensor.




Used some 5/8” hex brass to make some mounting nuts for the magnets. Simple lathe work here: Face, center drill, #7 tap drill, ¼”-20 tap, countersink the end with a 5/16” end mill, bore to diameter/depth and part. The nuts were flipped and chamfered on the side that butts up to the wheel as they were very close to a fillet on the wheel. Drilled and tapped ¼”-20 holes in the wheel, ran in cap screws, Loctite’d the nuts in place and secured the magnets with Loctite.


Faced and center drilled



Tap hole



1/4"-20 tap



Countersinking with a 5/16" end mill



Bored to size and checked fit



Parting



Flipped and chamfered the back side as the nut was just into the fillet on the perimeter of the upper wheel



Finished nuts



Magnet nuts and magnets were Loctite'd in place




Picture limit reached, so on to page 2 . . .


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## BGHansen

Next step was making a mounting bracket for the Hall-effect sensor. My original Plan "A" was to mount it to a plate that would be attached to a vertical bar on the left side of the saw. Problem with this idea is the wheel can be adjusted up/down about 6” of total travel. I scrapped the original idea as the sensor would need to be adjusted vertically whenever I changed blades (assuming my blades are not all the same exact length).

The upper wheel mounts to a shaft that can tilt to adjust blade tracking. This detail pivots on a horizontal shaft that is attached to a block that rides two vertical rods, a screw moves the block up/down to adjust blade tension. Plan “B” was to mount a bar to the sliding block going vertically and screw the sensor to it. Then me being my normal anal self was concerned about the plane of the upper wheel.  The plane is adjusted in/out at the top/bottom to adjust tracking.  If the sensor was mounted to a fixed point at the top of the wheel, it'd potentially have to be adjusted in/out as tracking was adjusted.  Granted, how often is tracking adjusted on the saw?  I had a Craftsman 12” band saw for 35 years and never had to adjust the tracking, but figured it was best to mount and adjust the sensor once and be done with it.


The upper wheel mounts to an axle with a through hole (3/8" bolt setting in place is I used a pulley puller to pull the wheel and didn't want to bugger up the threads).  The wheel axle is in a detail that tilts up/down for tracking.  That detail is mounted to a horizontal shaft that ties the tilting detail to the block that rides two rods for adjusting blade tension.  Drilled and tapped a couple of holes in the block for attaching a bracket for the Hall-effect sensor.




Plan “C” was to mount the sensor at the left of the wheel 1” above the wheel center axle. This is in-line with the center of the pivoting axle for the upper wheel, so tracking adjustments would tilt the wheel relative to the sensor but not move it relatively in/out to the sensor since the sensor is on the axis of rotation.

The bracket was made from ½” and ¼” aluminum on hand. There was a bit of poor planning on my part as the adjusting screws for the mounting plate were under the upper wheel. I ground down an Allen wrench to get the screws tightened and the sensor bracket position set.


Drilling holes to tie a piece of 1/2" aluminum bar stock to the blade tensioning block



Drilled and tapped mounting holes in the bar stock for attaching an adjustable plate which in turn holds the sensor



Milled a 1/4" adjusting slot in the 1/4" plate used to mount the Hall-effect sensor



Drilled a 1/2" hole for the sensor



Sensor mounting plate in place.  The sensor is on the center line of the shaft that the blade tracking detail pivots about.  This allows the sensor to be set ONE TIME and never touched as it moves vertically with the blade tensioning block.  It also doesn't change relative position in/out as the blade tracking is adjusted.



The sensor should clear the magnet in the brass nuts by 1mm-10mm, set it at about 1/8".  Spun the wheel by hand to verify clearance on all of the nuts.  Unfortunately, you can see just one of the two clamping bolts that lock the 1/4" mounting plate in place.  Yup, buried the 2nd one under the wheel.  Ground down an Allen wrench to get to it.  A smarter person would have put the adjusting screws in the openings of the wheel . . .




The tachometer is powered by 8-24V DC. This would be supplied by a 12V transformer. The saw is 220 V three-phase and is run off a static phase convertor.  It's wired with a DPDT push button switch to energize the phase converter.  The saw does not have a magnetic ON/OFF switch.  I leave the stock ON/OFF switch ON and switch the saw ON/OFF by powering up the phase convertor.  I added a 110 V box for the transformer by tapping into one of the 220 V lines (plus common and ground) in the phase convertor. This way the tach only comes on when the saw is powered up.

A ½” hole was drilled through the back of the saw to get the transformer lead to the tachometer. I made a cable clamp of sorts from a couple of pieces of plastic to lock the transformer wire in place. Another case of overkill on my part as a simple rubber grommet would have worked too.


Faced and center drilled some plastic stock for a wire pass-through



Turned the stock with a 1/2" shoulder in prep for threading



Undercut the base



1/2"-13 die used to thread the stock



Drilled and tapped a 1/4"-20 hole on the Bridgeport for a clamp screw



Back to the lathe for parting



Plastic clamp screw made from some plastic.  Turned a 1/4" shoulder and knurled



Threaded with a die



Parting off the screw



Finished pass through grommet/clamp.  Yes, looks kluged together. . .  They make pass-through grommets with a collet-type clamp on the end, but I'd have to order the right size.  I figure this is on the back of the saw so no harm, no foul.



Pass through grommet up top, 110 V box just below (need to pick up a steel plate to close out the outlet), static phase converter just below.





I'm nearing the photo limit again, so on to page 3 . . .


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## Doug Gray

Nice write up. Thanks for putting the time in.


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## markba633csi

I wonder if the tach has a cal adjust inside that could be tweeked to get the exact SFM ?
Probably not, it's likely done in firmware
-Mark


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## BGHansen

Didn’t show it, but the wiring was taped and tie strapped up high in the cabinet to keep the service loops from touching the blade welder just below. I also didn’t show it, but the bracket made by the previous owner for hanging the power cables was modified to raise the cables about a foot. Previously, the loops were right on top of the LOW/HIGH speed lever, much nicer set up now. 


Using a "Tubalcain" Bridgeport reference, the "ubiquitous" DoAll Job Selector wheel.  The outside spins letting you line up your material to be cut with the "windows" in the selector.  The selector gives recommendations for blade speeds, widths, tpi, and file info.



All fired up and working.  The original speed indicator has a note about reading out in "Feet Per Minute" and "Change Variable Speed Only When Machine is Running".  Last task will be printing a couple of peel and stick labels for the mounting plate.






Thanks for looking, Bruce


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## BGHansen

markba633csi said:


> I wonder if the tach has a cal adjust inside that could be tweeked to get the exact SFM ?
> -Mark


Hi Mark,

I looked inside the unit and didn't see a pot for adjustment.  On the plus side, being off by only 5% shouldn't be a big deal.  If it indicates 75 fpm, it's actually running at ~79 fpm.  I'd be surprised if DoAll adjusted the original speed indictors any better than that.

The saw is rated at a top speed of 1500 FPM, but I'm only getting up to around 1100 FPM.  With the 5% error, that's actually 1165 fpm.  I haven't dug into the back side yet to see what's limiting it.  Could be it is hitting that speed and the tach is off?  I have a Jacquet RPM meter and could confirm the speed.  Or just live with it the way it is.






Bruce


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## Ulma Doctor

a slightly larger motor drive pulley can put you to 1500 rpm, if you were really wanting the speed
but for metal cutting, you'll be ok IMO with the current ratio

nice work @BGHansen !!!!


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## NCjeeper

Enjoyed. Thankfully my tach is still working on my 1943 DoAll.


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## Aukai

Great write up


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## brino

Thanks for all the details and photos Bruce!

-brino


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## hman

I'm very happy to see that you made it work!  There's lots of fine detail between an idea and its execution.  A fantastic job (and great write-up) as always.


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## BGHansen

For grins and giggles, I ran a Jacquet RPM/surface feet checker on the lower wheel.  The Jacquet read 130 RPM or 544.5 FPM vs. my indicated 509 FPM (though with my 5% error, it's actually indicating 534 FPM).  Don't know which one is more accurate, but the new tach gets me in the ballpark.

Bruce


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## Janderso

Outstanding work Bruce.
I bet that's a handy upgrade.


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## BGHansen

Janderso said:


> Outstanding work Bruce.
> I bet that's a handy upgrade.


Hi Jeff,

Biggest thing it showed me is I cut with the speed WAY too slow.  According to the DoAll Job Selector, 1/4" 1018 steel would use a speed of 175-200 fpm with a 14 tpi blade.  I'd usually cut at around 75 - 100 with the same blade.  I did a trial cut on a 4" piece of 1/4" plate last night, not like cutting butter but made the cut in about a minute.  Lots quicker than my slower fpm.

Bruce


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## hman

Bruce -
If you really want to verify RPM, there are two things you can try.  (1) Verify the circumference of the wheel with a narrow (easily bendable) tape measure.  The nominal 16" diameter might be just a bit off, especially when you add the thickness of the tire.  (2) If you have a larger wheel for your turns counter, you can probably get a more accurate reading.  But both of these might come under the heading of straining at gnats.  It sounds like even the approximate RPM reading you're getting is starting to pay off!


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## Papa Charlie

Really nice job.


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## Papa Charlie

I meant to ask, what are you going to do with the old speedometer?


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## BGHansen

Papa Charlie said:


> I meant to ask, what are you going to do with the old speedometer?


It'll most likely set and gather dust from now to eternity. . .    Actually, one of our techs at work has it and plans on restoring it for sale on eBay.  He's pretty handy and has rebuilt speedos in cars for years.  He has an adjustable speed motor with a tach for a known reference to adjust the pre-tension on the needle's torsion spring.

Bruce


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## Papa Charlie

BGHansen said:


> It'll most likely set and gather dust from now to eternity. . .    Actually, one of our techs at work has it and plans on restoring it for sale on eBay.  He's pretty handy and has rebuilt speedos in cars for years.  He has an adjustable speed motor with a tach for a known reference to adjust the pre-tension on the needle's torsion spring.
> 
> Bruce


I was thinking that it would also make a very cool display on the wall. Glad that it will not go to waste.


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