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Shumatech DRO-350 Continued
3-12-2006

When I wrote my last update, I had 2 axes (X and Y axis) operational.  A12 inch Harbor Freight caliper on X and a 6 inch on Y.  Both were mounted using
High Density Polyethylene and I was pretty happy with being able to measure with a reasonable amount of accuracy.  With my Jenix 18" (450 mm) scale now here, it is time to install it on the X axis and move the caliper to the Z.  Little did I know that it would be over a month before that would be accomplished.

As someone on the Shumatech Yahoo group aptly said, "when you are used to the Chinese calipers, the Jenix scales look huge by comparison."  It's true.  The sensor part of the Chinese calipers are about 2 inches by 1 inch for the 12 inch model.  This means that the beam of the 12 inch caliper only needs to be 15 inches or so to allow for the sensor to read that twelfth inch and to have room for the caliper jaws.  On the Jenix, a scale that will read18 inches is over 24 inches long.  Of course, there are ball bearings to allow the sensor to track smoothly and the Jenix is enclosed in an aluminum shell to protect the quadrature decoding circuitry, and there are pliable wipers to help protect the insides, but it still looks big.

The Jenix came with some instructions and some examples of how to mount it.  There were also assorted pieces of mounting hardware,including some shims that I assumed were to set the distance of the sensor head.  The only trouble with these is that they weren't the same size as my sensor head.  This wasn't a problem for me as my bin of shim stock has plenty to choose from, but you may not be so lucky.  It appeared that the shims were for the larger versions of the Jenix scale models..  I am using the JSN5L version, which is the slimmest of their offerings.

Aside from this one omission, everything else I needed to mount the scale was included in the package.  The "armored" braided steel cable protector is really nice stuff and will do a great job of ensuring that nothing will cut the wires to the scale.  Now it was just a matter of installing the scale and soldering up a QCC-100 adapter for the ShumaTech DRO and I could check this thing out.

I had programmed all of the PIC12F629 chips when I was building my DRO-350s, so it was just a matter of soldering the components to the board, attaching the armored cable to the QCC-100 and ... Oh, DARN, no5 volt power supply lead!  Since the Jenix and QCC-100 are meant to run on 5 volts rather than the 1.5 volts of the Chinese calipers, I would need to bring a tap off of the 5 volt source of the DRO to the back of the case.  Darn again!  I really didn't want to have to open the DRO again.  Oh well, it was only about 15 minutes of work to add a jumper from JP8  on the circuit board to a connector on the rear of the DRO.

The next concern was one that I had thought about for a long time after installing the 12 inch caliper to read the X axis.  The mill's table has a slot along the front face that is used to hold the adjustable overrun stops for the X axis power feed.  When I installed the caliper in this spot, I was forced to mount the stops in a non-movable position that would just prevent the table's end caps from slamming into saddle if I forgot to shut off the power feed. I had experimented with positioning them and gotten them pretty close to where I needed them, but they were now not adjustable.  I was unable to reposition them to allow me to automatically stop the power feed where I wanted it when performing tedious multiple passes on whatever piece I was working on.  I missed this a lot and wanted to make sure that the Jenix scale was mounted in a way that I would have my adjustable stops back.  I decided that the way to go about this was to mount the Jenix flush with the edge of the table and with a bracket behind the ends that would allow for a strip of angle aluminum to cover the scale and protect it.  Outboard of the ends of the scale I would build additional brackets  to hold a 1 inch by .250inch thick slotted bar that would hold the adjustable stops. 

Another thing I had noticed was that I didn't seem to have as much table travel in the X axis as the Grizzly specs called for.  The specs on the sheet that came with the mill stated that X travel was
15.625" but the end caps on the table limited my travel to about 14.5".  It may not seem like a lot, but I wanted all of the travel that I can possibly get. While I was making up parts to mount the scale, I would also machine a bit off of the bottom of each end cap so that they would pass over the saddle, rather than run into it.  Machining a bit off of each of them would give me back about 2 inches of travel.  This would bring me up to about 16.5" of total X travel.  This is still well under the 18+ inches that the scale will measure.

Machining the cast iron end caps was pretty straight forward except for two things.  One is that cast iron dust gets everywhere and you have to watch out for hard spots in the metal.  I don't know what it is that is in this Chinese metal they call cast iron, but some of it cuts like butter, some of it is very powder-y, and some of it has what appear to be crystals and is hell to drill or machine through.  I used some of the last of my tapping fluid to get through this without dulling a second end mill.  The second thing was a bit of a surprise, but I guess that I should have expected it.  Before I started milling on the end caps, I used some paint stripper on them.  While I was scraping the old paint off, I was running into what appeared to be thick sections of paint.  Well, it wasn't paint at all.  It was bondo!  You know, auto body filler.  I realized this when the nice sharp corner on the cap came off and a chipped end was under that nice corner.  Filler seems to have taken the place of finish milling - at least on these end caps.  The sides of the caps are only roughed in.  The ninth picture down shows the chipped corner and the rough milling, if you click to expand it.  After I thought about this for a while, the use of body filler made sense, but it still bothers me.  With the end caps reshaped, it was back to finishing up the Jenix installation.

The instructions that come with the Jenix tell you that you should have a 1.0 mm vertical gap between the head and the beam and that the limit of error is 0.01 mm.  This would be pretty easy if you could do the drilling on the mill.  It is more difficult to do when you are trying to drill free-hand.  I ended up making a jig out of a piece of scrap steel and clamping it to the face of the saddle.  With this setup, I got the holes drilled to spec.  When I plugged in the Jenix scale and slowly turned the dial, I saw that the five ten-thousandths indicator did really work properly.  What had been a hit or mill proposition with the Chinese calipers, was working perfectly with the Jenix.  .000, .000-dot, .001, .
001-dot - the decimal point came on halfway between the next thousandth.  The calipers didn't do this accurately - even when they weren't hooked up to the DRO.  No matter how smoothly or accurately I moved the calipers, they would skip to the next thousandth without showing the decimal point at times.  With the Jenix, it was perfect every time.

I finished up the installation of the Jenix by adding the beam that would allow me to move the power feed stops.  I could have used those stops for machining the slot in the beam. Taking 0.020" cuts on each pass, I had to make about 25 passes to cut both slots.  Well, I will have the stops for the next project.

After working with the Jenix for a couple of days, I began to wonder if one of the reasons that the Chinese calipers wouldn't accurately show the ten-thousandths dot properly was that the calipers were not mounted as securely as they could be.  After thinking over all the possibilities and remembering that others have had problems with jitter due to not isolating the scales from the metal of the machine, I hooked up a jumper to see if that would be the case on my mill.  It didn't seem to make a difference, so I pulled of the Y axis scale and remounted it using aluminum, rather than the
polyethylene.  I also machined up a solid arm to connect the reader head to the saddle. This resulted in some improvement.  It was about as good as the unmodified 12 inch caliper that  I used on the bench.  It still missed the 5/10000" decimal point at times, but now when I stopped turning the crank, the measurement on the DRO didn't change after a few moments - like it did before.  Now, I could tap the head of the scale and the measurement would not change by a thousandth or so.

This got me wondering if the accuracy and smoothness of the scale could be improved upon by substituting ball bearings for the gib arrangement that the calipers come with.  I still hadn't installed the scale on the knee, so I took it apart, took some measurements, and drew up some plans.  Four flanged bearings on the bottom that the beam would ride on and four more unflanged bearings on top with adjustment to make sure that the beam was held securely.  It took about a week of evenings to complete.  It is markedly smoother than the stock caliper, but it still is not as accurate as the Jenix.  I ended up mounting it up, but I am seriously thinking of adding two more Jenix scales to the mill.  I think that they're well worth the price.

So, for the time being, the DRO project is done.  It has been a very neat project.  I have learned a lot and have ended up with a tool that is extremely useful.  Again, I have to say what an incredible job Scott did on the design and execution of this DRO. Truly top drawer.  It looks like I will be getting my second DRO out of moth-balls soon as I have just acquired another piece of equipment that would benefit from a DRO - a small South Bend lathe.




Jenix Scale
The Jenix JSN5L 450 mm scale.
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A QCC-100 gets assembled.
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Getting ready to machine the end caps.
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Done.
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An extra inch or so travel is gained.
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The Jenix scale is installed
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The angle aluminum is added to protect the Jenix.
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One bracket added for the new adjustable end stops.
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The second bracket.  Check out the nice chip in the end cap that was hidden beneath Bondo.
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Slots were cut and the beam is test fit.
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The beam gets its own slots.
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Testing the slots and captured nut behind it.
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I have adjustable end stops again!
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Adjustable with a hex head wrench.
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Same for the left side.
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One more view and a dark shot of the re-vamped Y axis mount.  Aluminum stock was used this time.
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Let's add some ball bearings to a Chinese caliper.
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The circuit board fits.
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Tab A, slot B, and put them together.
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A solid mount - 0.25 X 2.0" aluminum.
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The one-shot lube gets attached.
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Job finished.
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Next project!
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A 1934 South Bend 9" workshop lathe.
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Some goodies - including a milling attachment and the original 1934 literature.