Adding RPM sensor to Ditron D80 DRO and Takisawa TSL-800

[Winegrower]

I had an option to add rpm sensing and readout to the last D80 I purchased for $5 additional. That seemed too good to pass up. What I got was a Hall effect sensor and a few magnets...but no other instructions, other than one could use between 1 and 5 magnets and stay within 10mm of the sensor, and how to get the right polarity.

Two of the magnets were very tiny, little discs about 0.060 high and maybe 0.15 in diameter. I thought about a bunch of ways to position the magnets and sensors, and eventually decided to place the magnets around the spindle inside the gear covered area. I had a roughly 2" round of "Rulon", not sure what that is exactly, but a kind of Delrin type material. I cut a ring of it, the ID just being a "press fit" over the spindle, the OD just the height of the little magnets. I drilled two opposite holes in the ring just the diameter of the magnets, slipped the ring over the shaft and poked the magnets into the ring. Then, made another ring with the ID just a few thousandths less than the OD of the inner ring, and slid it over the first ring and the magnets, thus holding the magnets captive. It was straightforward to make an L bracket to hold the sensor and attach it using, opportunistically, an already existing tapped hole, of some originally unknown purpose. The tiny magnets need much closer spacing than 10mm, but it's non-contacting.

Then, configured the DRO for two magnets, and it worked perfectly. The RPM readout starts on the right RPM number and stays extremely stable...surprising me.

This has been a good $5 investment, though the Takisasa has a number of fixed speeds, so I already knew the RPM...just could not resist adding this feature.

This turned out to be a very clean installation. I like it.

 

[pontiac428]

Very nice! A linear encoder counts pulses, and so does a rotary hall sensor. DRO only needs a line of code to report RPM off of a normal input channel. What I really wish for is a RPM to SFM function. All that is needed is a diameter, but I haven't found a DRO that does this yet. It's too bad, the system has all the resources it needs to report SFM, just not the code.

 

[Winegrower]

What I really wish for is a RPM to SFM function.

You're right, that's a great idea! It's all there, if the X axis is set correctly.

 

[pontiac428]

I think the Far East DRO manufacturers are making so many sales for milling machines that they've forgotten lathes belong to their own class of tool. Most lathe DROs are called "lathe" because they have two scales. That's bogus, lathes can have six scales: long feed, cross feed, compound feed, RPM, tailstock quill and tailstock travel.

RPM can be coupled to cross feed. Vectoring for cross, compound, and longitudinal to track the tool point is already included in most lathe systems. And summing the tailstock position with the tailstock quill advance is another. That is a lot of axes, makes me wonder why the 2-axis systems even sell at all.

 

[Winegrower]

That is a lot of axes, makes me wonder why the 2-axis systems even sell at all.

That is a good observation. And, it sounds like a project idea! Wonder if anyone has set up a manual lathe like this?

 

[pontiac428]

I was thinking of doing a four channel (rpm, longitudinal, cross, compound) for the head side, and a two channel (quill travel + tailstock slide). It would require two full-length scales, one for longitudinal travel and the other for tailstock slide. Since the two never cross each other, it's easy to stack and stagger the linear scales. So if you zero the tail and quill at the chuck face, you will always have the distance to the chuck face when working with the tail stock. That would be great for boring and drilling.

For features, I think the only thing I care about (beyond vectoring and sum/difference) is radial/diametric mode switching, which most every DRO has already. It's a shame to have to make this work on two head units, though. It would be nice to have measurements like distance to tailstock center from the tool tip calculated in unity.

Then again, I've been just fine for years on the lathe using only hand wheels and calipers. It's easy and natural. Maybe DRO is overthinking it, especially if there aren't many useful lathe-specific features to implement. Yuriy Croosh @ycroosh would be good to talk to about this, but I think my big industrial grade lathe needs industrial quality encoders and scales.

 

[MrWhoopee]

Rulon is , IIRC, a Delrin/teflon blend. Kind of like Delrin AF only prettier. Price tracks gold pretty closely.

Rulon (plastic) - Wikipedia

en.wikipedia.org

 

[B2]

Being a newbie I did not realize that I could get a DRO channel which did RPM. I wanted both RPM and rotation counts (for winding coils etc). So when I was doing my VFD install I incorporated a Hall sensor driving two displays. One for counting rotations and one for RPM. I needed a physically small counter display to fit the front panel and found one and it had lots of digits (6) so I put in 10 magnets to make it easy to figure out. So my RMP meter and counter are 10x.

You can see a photo of the counter and the RPM meter in the lathe front panel here:

As I mentioned before I was adding a counter to my VFD converted PM1440GT.

If you go the beginning of this post string you will find other pictures, including one of the Hall sensor (Fig 10a photo) and the 10 magnet mount. It is larger than it needed to be since at some point I plan to mount a spider and will cut the inside diameter of the magnet mount to be larger. The green material is nylon. It is split so that it will fit over the spindle and has a nylon bolt running through the split.... that magnet holder to the spindle. The first posting did not include the counter so that photo is at the link. page 3. There is another posting where I built a nylon backer board for my mill and made the front panel plate and this Hall magnet holder. The magnets could be smaller and still work fine, but these are about the size of a dime and are over kill.

By the way, there is a third digital display shown at the left, which shows the voltage being applied to the VFD to set the speed. It is calibrated to Hertz and so shows the frequence prior to the lathe running. This way I know where the VFD pot is set.... approximately. (10x, 1volt=10Hz)

Dave L.