Dial Indicator Adjustable Arm Extension for Unimat Lathe

[Paul Jones]

Space is limited for using a dial indicator (DI) on my small 3” swing Unimat lathe for 4-jaw chuck setups. Most of the lathe is made from non-magnetic parts and also has very little room to attach a magnetic base where there are ferrous metal parts. Using a boring tool holder in the QCTP (quick change tool post) works but this requires changing the cutting tool holders and possibly resetting the previous tool position (see photo below).



My solution uses a separate adjustable arm extension and attachment bracket for a small Noga adjustable arm DI holder with an 8 mm clamping rod. The adjustable arm extension is made from ½” square 6061-T6 aluminum and 12L14 steel rod materials.



The Dial Indicator Adjustable Arm Extension parts were created using the milling head to the 3” swing Unimat lathe, a 7” swing mini lathe dedicated to collet work and a 12” swing geared-head lathe. These are the parts for the Dial Indicator Adjustable Arm Extension.



I designed the riser blocks for supporting the Unimat SL lathe on a small cabinet. The riser blocks include several pairs of 6-32 threaded holes along the block sides and ends for “future” attachments to the lathe. I am already using one pair of threaded holes behind the headstock to hold the detent arm support to the dividing plate (see http://www.homemadetools.net/indexin...nimat-sl-lathe). Using a similar method, I added support brackets to the headstock and tailstock riser blocks and still have plenty of pairs of threaded holes for other uses.



The aluminum rod extension made in two parts is ½” square and 4.5” long with a 8 mm rod clamping end and a shorter piece 2.5" long for allowing side-to-side adjustments. The clamping end has a 8 mm by 2” deep hole that is externally threaded ½ X 20 and with four 1.1” long jaws formed from the slots. There is a knurled 12L14 steel collar internally threaded and with a internal tapered end to compress the four jaws. The 8 mm rod of the Noga adjustable arm DI holder fits into end with the four compression jaws and is clamped in place with a internally threaded collar. Note: before finally assembly, an 8 mm dia. drill was used to "cleaned up" the 8 mm by 2" deep hole after partially threading on the knurled steel collar (not yet to full compression) to ensure an exact fit for the Noga 8 mm support rod.



The four slots forming the jaws were cut with a 0.045" thick abrasive cut-off wheel and Dremel tool while the aluminum arm extension was held in the lathe using a 4-jaw chuck. In this operation, my 12” swing lathe could have use the lathe dividing head designed by Christophe Mineau (see http://www.homemadetools.net/forum/%...e-cranck-41391) but I substituted a Starrett combination square protractor level and soft jaw adjustable clamps to do the dividing. When I was a teenager in the early 1960’s, I taught myself the basics of machining by reading many used books for the 1930’s and 1940’s about machining. I think the use of levels was far more prevalent than we see today and is often overlooked. I checked my protractor level work with a 0.0005”/foot master precision level (and previously used to level the lathe) and it is very accurate.



Lately on HMT there seems to be a theme of showing Dremel tool uses and below is another photo of a Dremel tool at work. It is cutting the slots for the clamping jaws with a 0.045” X 1.5” reinforced abrasive cutoff wheel. The abrasive wheel easily cuts through the aluminum but is partially consumed in the process and the dial indicator measuring the carriage travel is no longer valid for determining where to stop the cut. In this case a visual stop and don’t rely on depth stops or dial indicators whenever the diameter of the abrasive wheel is diminishing. Also, the lathe was protected from the cutoff wheel grit using paper towels and bulletin board magnets.



FYI - The Dial Indicator Adjustable Arm Extension is attached to the risers blocks I previously created for the Unimat lathe. At the time I anticipated adding more accessories to the lathe. I added pairs of 6-32 threaded holes to accommodate these future accessories. See the photos below. I plan to post more article about other special purpose parts that will be attached to the Unimat riser block including a power feed attachment.

Photo below shoes the pre-threaded 1" square lathe riser block for attaching lathe accessories.




Photo below shows the mounting bracket for the adjustable arm extension attached via 6-32 socket cap screws to the riser block.



Thank you for looking,

Paul Jones

[MetalDesigner]

Well Done!! Great Project ... The parts are like artwork!!

CHEERS!!

[Paul Jones]

MetalDesigner,

Thank you. I think I have the lathes so well adjusted and finely tuned that the finishing cuts no longer need any further polishing or improvement. What you see is the actual machined surfaces.

Thanks, Paul

[bstanga]

Outstanding work Paul!

[DIYer]

Thanks Paul Jones! We've added your Dial Indicator Adjustable Arm Extension to our Lathe Accessories category,
as well as to your builder page: Paul Jones's Homemade Tools. Your receipt:

Dial Indicator Adjustable Arm Extension by Paul Jones

tags: lathe, dial indicator

[Christophe Mineau]

Great, I like the way you take time to explain things Paul, and your finishing level is really impressive. I wish I could reach the same ... And I like the way you did the collar chuck, especially with the Dremel wheel, I would have done the same, I also find the Dremel on the lathe very useful.
For the protractor level I also totally agree, and we could add that if possibly more accuracy was needed, it is always possible to put a straight edge on top of the chuck jaws and check with the level at the extremity of the straight edge, but obviously not necessary for your application.

May I ask a question, except for the beauty of it, why didn't you use a simple set screw for attaching the arm of the DI instead of the collect chuck ?
Thanks,
Christophe

[Paul Jones]

Christophe,

Thank you and an excellent question about the use of a set screw. I originally wanted to use a cap head screw and offset the 8 mm hole closer to one edge of the 1/2" square shaft so there would be room to tap threads. In all the modifications to the Unimat, I have standardize on 8-32 cap head screws and M6X1 cap head screws for tightening parts to allow for only two sizes Allen wrenches. The size differences allow picking up the correct wrench the first time.

The real reason I used the collet chuck is because it will be used in some of my future projects and I just wanted to see how to make one. There is one step in the chuck fabrication I thought might be a problem but I found a work-around. The 1/2" shaft is pre-drill to 8 mm x 2" deep (sorry about the mix of measurement systems but I am use to working in both systems) but there is some inward compression after slotting for the compression fingers (chuck jaws).

However, after partially threading on the knurled steel collar there is slight (a few thousands) of inward compression on the four jaws before reaching the internal taper-end used locking the 8 mm shaft. At this point the 8 mm shaft of the Noga DI holder won't slide in. I made a 0.375" thick washer as a spacer that temporarily prevents the knurled collar from threading all the way and reaching its point of compressing the four jaws. I then re-drill the 8 mm hole (or use a spiral fluted reamer), removed the spacer, threaded the knurled collar back on but not fully tightened. The 8 mm shaft slides in freely until the knurled collar is tightened to full compression and locks the shaft.

I hope this makes sense. Shown below are photos of this final operation using the temporary spacer to prevent the knurled collar from closing down completely on the chuck jaws.



Cleaning up the chuck with an 8 mm drill to ensure a sliding fit to the Noga 8 mm shaft



Thank you for the question.

Paul

[PJs]

Thanks Paul and Christophe (good question). Had the same thoughts but really get trying to "make a collet chuck". A skill set and technique that is handy for all kinds of projects. Standardizing wrenches is way smart thinking IMHO. It's a pain to have 5 different ones at hand while on a project.

Thank you Paul for the overall build with the detail on the collet build and the nuances to it! ~PJ

[rossbotics]

Hey Paul
Great looking work and write up as well, that's a cool little setup you got there, nice work on the parts you made, they look outstanding, If you make a mistake now it's your fault ! LOL

Cheers
Doug

[Paul Jones]

Thanks Doug,

The thing about mistakes when working on your own tool projects is these can become additional features (or not ).

Last night, I weighed the "cool little setup" and discovered it added some weight in the last year with all the new tooling and attached parts. What you see in the first and second photos (lathe, milling head and cabinet full of tooling) now weighs 60.5 lbs. I would have never guessed the weight.

Thank you,

Paul