ToAuto DRO Glass Scale add-on to a Jet JMD-15 End Mill

[CDBEAM]

Hello All !! I hope everyone is safe and well !!! I was not sure where to post this adventure....but decided to post in the Beginner's Forum as this seemed the best fit !!

Well….I decided to purchase and mount the ToAuto ( China made) DRO unit to my Jet JMD-15 End Mill. Regarding the MD-15 End Mill…I should have purchased the JMD-18 ….or found an Old Iron used Mill !!! But…This End Mill has served my purposes for at least 8 years….and been a great first Mill. Yes…to some…. it may seem….the Jet JMD-15 is a glorified Drill Press…and the China scales…sheeezz !!! Well….we all have to start somewhere….and, like I said, for me….this is fine. The JMD-15 is limited…OK…Quill travel is too short !!….but the entire Head unit can be raised and lowered. Regardless…I have found the JMD-15 is more than adequate for my size needs, has very tight tolerances ….BUT... the unit needed a DRO !!

So….To start…I am very pleased with the quality of the ToAuto DRO !!! It is well made and heavy duty. Of course, time will prove the unit reliability….but…..good price, very large read out, many added computation features, accuracy @ 5um, metal cable runs between DRO and scales….All good….as far as I can see !! I purchased the scale sizes; 350mm, 450mm and 950mm. See attached pics !!

It took me some time to figure out the attachment pIan !! ….That was a challenge !! I used the 950mm scale on the X axis, the 450mm scale on the Y axis and the 350mm scale on the Z axis.

For the X and Z axis scales, sections of 1/4” x 3/4” Aluminum bar were used to attach the scales. I was successful in using ONLY existing bolt holes for all scale attachments. That was more luck than inspiration !!

For the X axis….a long section of bar stock was attached to the ways. I attached the stock using the ways travel bolt limits blocks to attach to. The Ally bar bolted up tight the front facia of the ways. The Ally bar extended past the end of the Way (was equal to the width of the 950mm scale body) and the scale body was then attached to this bar. An additional short section of Ally bar stock was bolted to the location where the T shape way stop was originally located. This worked well because both Ally bars were then on the same vertical plane. The Scale head was then bolted to this shorter section. I should note that the scale body is above the scale head in this mounting.

For the Z axis, again a 1/4” x 3/4” Aluminum bar was used. A section of Ally bar stock was attached to two (2) existing threaded holes originally used to secure the Belt Speed Selection placard. The scale body was then attached to this bar. A Small Brass block was then machined ( L@1.25 “ x W@1.17” x H@0.50” with a 0.50” bore thru) and secured to the original vertical height indicator threaded rod. The scale head was then secured to this Brass block via a small Ally angle length.

Finally, the Y axis…..which was the most difficult….was the last to do. I used one of the two existing bolt holes used to lock the ways in the Y axis. I felt that the remaining lock bolt should be sufficient to lock the ways Y axis movement ( Seems to be). I machined a small Ally block ( L@1.64” x W@1.64” x H@1.01”) to act as a stand-off. This stand-off was bolted to the carriage via the existing bolt hole. A short section of Ally bar stock was then bolted to this stand-off block. The scale head was then attached to this short section ( see pics).

SO…I was wondering how to secure the scale body to the Mill base. I decided since there are four (4) bolts used to bolt the mill to its stand…..I would use the two (2) on the right side to secure the scale body. I machined an Ally angle stock to 1.3” x 2.0” x 20”. This angle stock was then secured to the JMD-15 unit base by removing the hold down bolts and capturing the angle and this then bolted the angle to the base. SO….the the Y axis scale base was then bolted to the angle stock front and back. All scale heads traveled straight and with ease.

As a final detail, the DRO readout unit was mounted to the existing Fwd/Rev/Off selector switch box stand-off bracket. Seemed like a good location that I could bolt the mounting bracket to. I may do some cable bundling….but…nothing other than that. Originally, I thought the cables were way to long. That is not the case.

SO…It is done !!!….and works perfect. Wow….What luck !! To anyone thinking about adding a DRO to their Jet mill….well….THIS is one way to do it !!! Challenging !!! ….But… I think a very worthwhile project !!! Face it….many beginners may start with a Jet Mill…. And a DRO is a great add-on !!!! The most difficult job is how to attach the scale body’s and scale head’s to the Mill !! I decided to share my adventure after a search of the Forum archives with no real specifics regarding a Jet Mill and DRO attachment. Hope this helps someone…sometime. CDBeam

 

[compact8]

You may want to turn this scale upside down to avoid swarf or cutting fluid going into the internal of the scale. The plastic seal on the scale may not be completely reliable to prevent this from happening.

 

[compact8]

You may also consider calibrating the scale. Mine is off by 0.04 mm over a length of 100 mm. The panel has the function to compensate for the error.

 

[addertooth]

I will agree with others on the orientation of the scales. Always have the "read head" facing Away from the spindle (the key source of chips and swarf). This is true of your Z axis as well, the read head should face Away from the spindle. It does complicate the mounting mechanism a bit. Those falling/spraying chips will find a way past those seals and foul the glass rod, and cause real problems.

If you keep your orientation, it may also require you go into your settings to Reverse the reading of the axis as well. i.e. Z axis going UP should create positive climbing numbers, X axis table moving Left should create positive climbing numbers, Y axis going towards the operator should create positive climbing numbers.

Some of your scales are a bit "oversized" for the range of travel your mill has, but no harm, no foul. You likely got them as a "set" at a value price. I can perfectly understand your resistance to drilling and tapping holes in your mill. The forums are replete with stories of people who broke drills and taps, while trying to create threaded holes in cast iron. But, I think you should treat a mill/lathe like a hot girlfriend. Don't be afraid to drill it, because you are trying to keep it pristine for her next boyfriend. Certainly keep her lubed and clean, but don't be afraid of tapping it.

 

[addertooth]

As Compact8 said, check your calibration too. If you have the 5 micron scales, then the minimum (typical) change will be 2/10,000ths of an inch.
Set up a couple of 3-2-1 blocks end to end (6 inches long) with a edge finder. Add the thickness of the edge finder to your expected length (my edge finder thickness was 0.200 inches), for an expected reading of 6.200 inches. If you are plus or minus .0002, that is fine. It was likely a flea's eyelash away from jumping to the next number. Use that value to calibrate your scales. The formula for changing calibration is in millimeters, and NOT inches, so you will have to convert inches (accurately) to millimeters. Do this calculation to at least six past the decimal point for optimal values. (Don't just use 25.4 mm per inch).

p.s. Don't be surprised if you learn your "hand wheel measurement" vary from the DRO; this is not uncommon. The hand wheel has greater variables in heat expansion than Glass. Also, some have discovered the lead screw was not manufactured to the accuracy they believed, once they put on digital scales which have been carefully calibrated. They falsely assume their digital scale is off. But, if you have precise and known standards which you calibrated to, then trust the digital measurement MORE.

 

[Papa Charlie]

I need to go back through the manual that came with my ToAuto DRO, I don't remember a calibration portion, but it has been a while.

 

[Watchwatch]

Use a dial test indicator to edge find. And I’d also recommend a using a gage block instead of 1-2-3 blocks. A pair of 123 blocks can easily be off .0005. You can add in another .001 for edge finder error.


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[addertooth]

Use a dial test indicator to edge find. And I’d also recommend a using a gage block instead of 1-2-3 blocks. A pair of 123 blocks can easily be off .0005. You can add in another .001 for edge finder error.


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WatchWatch,

I was trying to suggest using tools which most people would own. As for the accuracy of a good edge finder, most are good to a couple tenths of thousandths of an inch. I would throw away (or clean) an edge finder that was only good to 0.001 inch. Many inexpensive test dial indicators which are owned by the average joe, have some Slap/slop, before the needle starts to move. Now on a higher end test indicator, the needle starts to move at less than a tenth of a thousandths of an inch. I trust my Starrett Last Word indicator significantly, but, it was important to show doing this test with more approachable (less expensive) tool sets.

And yes, you should take a micrometer to your 3-2-1 blocks (and edge finder) first. That will establish where the tenths of thousandths settle out. I was trying to keep the example simple. In my case, the errors in size cancelled each other out, but I did not want to load these posting with details that would detract from the general concept. I also left out the thermal expansion/contraction of the finder/blocks... versus the smaller variation of the glass rod in the scale. I didn't want to muddy the water with that esoteric calculation either. I also did not mention the "wobble" even a precision collet/spindle has, which subtracts from the measurement as well. Once all of those were factored in, The "corrected" was actually 6.200, but once again, that is all muddying the waters. Normally calibration is to eliminate errors in the thousandths, which likely exist before calibration.

In the end, unless he is making a seal for a space shuttle, an error of 2 tenthousandths over a distance of 6.2 inches, is close enough for a hobby mill.

 

[compact8]

I need to go back through the manual that came with my ToAuto DRO, I don't remember a calibration portion, but it has been a while.

The manual I have got does have a section on calibration. They have linear calibration as well as non-linear but I think the former should be sufficient. Chinese products are very well known for their poor documentation. This youtube video may help :

 

[jwmelvin]

(Don't just use 25.4 mm per inch).

Er, I think it might be hard to use more significant figures for that one.