How to get correct speed and full range from 2J2 variable speed drive?

In an earlier thread, you all (and the outstanding folks at H&W) helped me get my recently-purchased BP with 2J2 head running smoothly. Since then I have only had bits and pieces of time to do some additional fine-tuning.

One thing that I was pretty sure needed adjustment was the speed setting - based on the "feel" and how cutters were cutting, plus the fact that the speed setting screw was all the way out (I left it where it was set when I got the machine), I suspected that the speed was significantly off as compared to what it showed on the dial. I finally got an inexpensive laser tachometer, tested it against various spindles and rotating objects with a known speed - seems pretty accurate across a broad range, certainly within a few rpm - then I tested the BP spindle. Turns out the BP spindle was turning nearly twice as fast as what the dial said! My lowest speed in the high range was not 500, but around 975 rpm.

No problem, right? Just loosen the locknut and adjust the screw. Well ... problem. I had to turn the adjustment nearly all the way down to get the speed down to 500 (and likewise to 60 in back gear) - but at that point, I'm getting a scraping sound; I'm still trying to figure out a way to see what's going on while the machine is running (hard to see when the head is assembled!), but presumably either the yoke is scraping against the pulley, or maybe the belt, being squeezed out to the maximum possible, is rubbing against the adjusting chain - ? While I was contemplating whether I could live with that, and/or how to create clearance, I tested the higher speeds. Oops - it ran smoothly from 500 up to around 2000, but then further adjustment had no effect. Even though the dial turns, and the chain loosens, it seems as though maybe the yoke just can't tilt any further, or something else prevents it from moving any further. For what I do, 2000 would be plenty of speed at the top end ... but here's the problem: This means that in back gear, it tops out at 200 or so rpm - leaving me with a gap from 200 - 500 rpm.

I've tried adjusting the speed adjustment screw in various ways, hoping to at least wind up with something close-but-usable (knowing I could rotate the dial to try to compensate) - but so far, unless I adjust it way back up (way over speed), I seem to "top out" at some point, and thus have a gap in my speed ranges. I wonder if the shop I bought it from intentionally set it up at approximately 2x speed, and just calculated the actual speed accordingly - ?? However, this would mean the lowest speed would not be 60 rpm, but 120. Maybe I don't need 60 rpm ... ?? But ideally I sure would like to have the stated range of 60 - 3000+ rpm.

One obvious question is whether the motor is turning the right speed. That brilliant thought didn't occur to me until I was typing this - so I will try to get out and check that sometime today. But it does appear to be the correct, original motor, and at least visually it doesn't look like it is spinning 2x too fast. And yes, it is properly wired for the 240v 3 phase that it is receiving. (And even if not wired correctly, the wrong voltage should not change the rpm, but just fry the wiring, right?)

So ... is this a common issue with this head? Are there any brilliant solutions? Maybe something in the chain or yoke attachment or something like that needs to be adjusted ... ??

The chain for the speed adjustment can only have one thing wrong with it and that is installation error. When a head is reassembled the chain is wound in the wrong direction around the spool before screwing the assembly back on the head.

awake describes a problem with the head that when a top speed is reached it is under the maximum rpm and that the speed adjuster has no tension. This describes a problem with the drive sheave sticking on the shaft.
When the movable sheave on the motor shaft sticks the problem is usually the key.
The key could be sheared, typical for a 1 1/2 hp mill or it could be a broken capscrew on a 2 hp mill.
When this happens the sheave cannot move to full extent of travel and the speed dial tension goes limp.
If while taking a heavy cut and the rpm drops off this is an indication of a sheared key.

John

John and Car, thanks for the responses. The belt is brand new, as are the bushings and keys. I do get a full range of response when the adjustment screw is all the way out; it's just double the expected speed.

I have definitely contemplated cutting in an inspection window! But I'm hoping for a less invasive solution...

Sent from my SM-T230NU using Tapatalk

There already is an inspection window if one needs to see the location of the belt w/r/t an rpm.
Stop the mill and remove the speed change plate. Unwind the chain for a look inside.
Remember to draw the chain up with a bit of tension after peeking inside. Else the
vari-disc will have a snap speed change because of the slack.

Thinking about the original problem and taking a peek.
Why not run the mill up to the 2000 rpm limit. The point where dialing up the rpm has no further effect.
Then pull the speed plate and see if the belt is at the inner diameter of the vari-disc.
To get to the 4,500 rpm range the tension is released on the front movable vari-disc. This lets the spring
on the motor shaft force its vari-disc upward. As the vari-discs on the motor shaft approach each other the
belt has to run close to the outer edge of the vari-discs. At the same time the the vari-discs on the driven shaft
are separating until the belt runs at the smallest diameter.

Turn the power off.
If the belt is not at the smallest diameter it is possible to manually position it.
With the speed change plate removed, rotate the spindle manually. A drill chuck with a key handle stuck in one of the holes will do.
Give the chain some slack and rotate the spindle. Actually one can reach in the and force the belt into position if there is enough slack.
If the belt does not draw up tight while rotating the spindle the problem is on the motor shaft.
If so:
The spring retainer plate is hitting the keyway. I had to pull the motor after a rebuild once and this was the problem.
Take a look at the key and keyway on the driven shaft.
Check the fit of the movable disc on the driven shaft. I usually added a fine film of Mobile red synthetic grease here when installing new bushings. I like to re-curl the bushings to a smaller diameter so they hug the shaft tighter when the epoxy hardens. Without the grease they might drag a little. I like em tight. They last longer.
I don't remember the height of a new spring. Ask Barry and compare it to the height of your spring. I have changed springs but this is not a very common problem.
In the first diagram in post #3 look a #17, 18, and 19, there are two of each total for left and right side of the plate. These guys allow the plate to rock and if the special washer is not there the correct speed cannot be set.
What is the nameplate motor rpm?
John

Thanks John, very helpful. Unfortunately it will be a couple of days at the earliest before I can test out the various possibilities. I'll report back as I find out more.

By the way, I have indeed been using the "inspection window" available by removing the speed adjustment - but that doesn't let me see all that I would like to see. But the suggestion about checking how far out the belt is going at the different speeds is very helpful indeed, as well as seeing if there is a way to move the yoke after it "tops out."

I'm resigned to the likelihood that I'm going to need to open it back up (pull the motor and the top cover) before I'm done - fortunately, having done it once, it is not at all hard to do again - and this time it is clean, rather than absolutely filthy with old grease and oil and grime!

Brief update - I put the tach on the motor, and measured around 1780 rpm. The plate on the motor says that its speed it 1410/1710. That surprised me greatly at first, but on checking the math, it would seem to be about the difference between running at 50Hz vs. 60Hz.

So if the tach is accurate, the motor is running a little fast - but not anything like 2x fast. As for the accuracy of the tach - I certainly can't guarantee that it is accurate at every speed and at all times, but in numerous tests of known speeds, it is dead on. Also, I took the spindle down to the slowest speed in back gear, slow enough that I could count the reflective strip as it revolved and time it against a stop watch. Again, the tach agreed with my direct observation.

Haven't had time to do any more, and probably won't for another week or more -- too much else on the schedule.

Did you solve the problem? I'm replacing a variable speed plate so I'm following along. I did buy a cheap tach reader from Harbor freight and it was all over the place. I returned it and bought a starret rpm indicator for $13 there was a few of them on there from $15-$25. Plus it's a starret!! Make sure and find one with all of the heads with it. Mine came with 5 but there were a few with none or one. Good luck

Oh... my head was making a ton of noise and my rpms were all over the place. My variable speed plate and sliding housing had a ton of wear on them. Atleast a 1/4" of wear!!! Somebody replaced the screws and used washers instead of the correct ones. My bearings and everything are still like new which is a relief but I am trying to figure out if i can use the bridgeport plate and housing in my Alliant. There is a $100 difference on the housing between bridgeport amd Alliant. Sucks

The Bridgeport speed change plate rocks forward and back via the Pivot Sleeve #19.
The sleeves are secured to the bearing cartridge with cap screws. The location of the
sleeves acts like a fulcrum for the plate.
Don't know if the plate can be interchanged with an Alliant mill.

John

Sharp (who purchased Alliant ) sent me the diagrams, I think one of them was hand drawn lol. I have all of that figured out now just trying to see if I can save a $100 by buying Bridgeport parts instead of Alliants. I'm probably going to go that route and either bore out the housing or shim it. They look identical from all of the pics I've found so far. I probably wouldnt be looking if they would of just used the correct sleeved screws in the first place. Someone used regular screws with washers and it didn't work out very well to say the least. I bet that's why they sold it. I bet they thought the bearings were bad. The culprit was the prior fix. Smh!! Thanks for the reply I really appreciate it. If they do swap straight over I'll put a post up letting other guys know about it. Have a Merry Christmas, Ty

Tystick77 said:

Did you solve the problem? I'm replacing a variable speed plate so I'm following along. I did buy a cheap tach reader from Harbor freight and it was all over the place. I returned it and bought a starret rpm indicator for $13 there was a few of them on there from $15-$25. Plus it's a starret!! Make sure and find one with all of the heads with it. Mine came with 5 but there were a few with none or one. Good luck

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Hello Tystick,

Yes, for the most part - I made new sleeved bushings for the screws and a new adjustment screw, and TIG-welded to repair the wear in the yoke plate. Here is the thread with the information: http://www.practicalmachinist.com/v...-2j2-speed-adjustment-plate-okay-weld-338817/