How to mount encoder on the Bridgeport spindle?

It seemed much more messy before I did it, now that I have done it it seems a lot simpler than I thought.

See

pictures, etc.

This was on a Bridgeport 1J head, the step-pulley version. The varispeed version has a more complicated arrangement, where I believe the bull gear moves up and down instead of the pinion. You might still be able to find a position for the quadrature sensors that picks up the gear teeth in both positions. But, the index sensor would have to have a flag that trips the sensor both ways.

Bridgeport didn't make this a drop-in option, that's for sure.

Jon

A releated question...

What is the desired resolution required to support rigid tapping? How many "ticks" per revolution?

-Wayne

J>

I went with 500 ct, mainly cuase I found an AB unit on eBay cheap. Low res. is best cause you need to read it at 5000 RPM.

I didn't worry about the backgear thing and put it on top by using an expanding arrangment to clamp to the hollow spindle bore. Mine was trick cause I needed the tool changer to still work. Iggy, as you're not using a tool changer, this would be a piece of cake. I have a prox sensor on the backgear switch to know which gear.

Jon's method on the spindle itself would be better, far more work to install.

Karl

Karl, this is my $64,000 question, what expanding arrangement did you use?

I spent several hours with what I thought would work well, a rubber plug with a bolt inside, but it was extremely eccentric.

So I am looking for better accuracy.

i

This is what I made for a stop to fit inside my collet closer tube.

The 10-32 screw clamps onto a 1/2" rod, the 1/4-20 expands the 1.100 diameter inside the closer tube. Substitute the encoder shaft and inside dia of the BP shaft for those dimensions and you should be good.

Not I know why it was eccentric. This is some kind of a translucent urethane piece from mcmaster that is 1" thick and has a 3/8" hole. I would insert a 3/8" bolt and tighten it and it would be eccentric.

Turns out that walls of it are not uniform thickness. One side is thicker than the other.

i

Jon, Karl and Ned, I bought this on ebay for $41 (best offer).

I will try to use it by hooking it up to the actual spindle (not the inside of the driven pulley), for always 100% accurate measurements. The spline will spin and move up and down with the spindle, whereas the sliding thing will spin and stay in place, driving a little pulley to spin the encoder.

i

Can EMC2 keep up with 500ct at 5000rpm? I know tapping does not occur at that speed.

-Wayne

IIRC, my unit is just like Ned's. Pretty standard way to expand clamp something.

Looks like you found another way, based on another part of this thread.

Karl

A rod, very close fitting, with an o-ring groove and o-ring to cause it to grip to the hollow shaft. Use more o-ring grooves and o-rings if you have slippage during start/stop Easily removable.

Wes

OK, this seems to be a good option. I would like this to be a tight fit, so that I would have to use a hammer to push it in, and a puller to pull out.

The shaft is 25.94 to 26mm ID. Given that, what would be a good option for O ring diameter (ID and OD), so that they would compress properly.

I am thinking to buy 26mm O rings from McMaster, and make grooves so that the O rings are slightly stretched and stick out to perhaps

26.5mm.

I also see a lot of rubber tube expanding plugs at Mcmaster. I am thinking that they may provide the easiest option.

i

I am still deciding. I want something easy, that I can also quickly undo.

i

I don't know if it will fit your application correctly but there are keyless bushings that expand on the inside and outside, like to hold your encoder shaft or spline shaft to the bore of a spindle.

RogerN

I really don't think it needs much. The bull gear on a Bridgeport 1J has

81 teeth, so you get 324 quadrature counts. That seems to be quite fine for the tapping I have done.

Jon

Can't say for every user's setup. The encoder counter Iggy is using is my PPMC, which clocks at one megaHertz, so it should reliably count pretty close to 500,000 counts/second. 500 counts/rev * 5000 RPM / 60 = 41667 counts/second, so no sweat. even if it was a 500 CYCLE/rev encoder, giving 2000 counts/rev, that would be only 166,667 counts/second, so still no problem.

I don't know what hardware assist Karl is using, but at 42K counts/second, a hardware encoder counter would be a good idea, it is at the upper limit of software encoder counting.

Jon

start/stop

What I'd do is make an expanding inside collet. Turn material to just fit the ID of the spindle. Drill the canter, then tap for a suitable thread. Then, drill and bore a taper in the ID. Finally, slot the part with two slots at

90 degrees, on the end with the taper, down to where the thread starts. Now, make a screw that fits the thread and matches the taper. When you screw the tapered screw in, it expands the collet, locking it into the work. I've made these for some custom turning projects where I wanted to face both ends and turn the entire diameter of a part in one setup. They worked like a charm, and were not hard to make. It almost takes longer to explain than to make.

As for your specific job, I'd put a slot in the bottom of the collet so a screwdriver can be stuck up into the spindle to hold the collet while you tighten the top. You could make the rod that drives the encoder be the same part as the tapered screw that expands the collet. It might be easier to make the encoder move up and down than to use that ball-spline.

Jon

The US Digital encoder that I have, has 1,024 pulses (or 4096 counts), so, at 4800 RPM, it will be 4096*4800/60 = 327680 counts per second. Of course, I would never tap at 4,800 RPM, and in fact, I will tap in back gear only, under 450 RPM, so I get 30720 counts per second at most when tapping.

i

If your orings are slightly large as far as circumference, you can trim with a razor and glue them back together again with isocyanate adhesives (Crazy Glue) although I'm fond of Loctite 411 myself since we have it at work.

Wes

-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller

Does anyone here truly have that good a luck with crazy gluing? I get a 25% "stick" rate with liquid and about a 66% rate with gel, and I've tried gluing many different things with many different $1 packets of super-glue. Is my horrible failure rate due to cheap adhesive, or am I just doing it all wrong? I've tried primers and thick, medium, and thin usage, most to no avail.

LJ--Unstuck in Oryguns

-- Know how to listen, and you will profit even from those who talk badly. -- Plutarch