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Drill Press DRO

Been wanting to add a depth indicator to my drill press for a long time now, and eliminate the need for Drill Stops, Sharpie or painters tape on my bits, none of which are very accurate.  I futzed around with using a dial indicator but it never really fit because of the size and limited range.  Keeping in mind this is a cheap n' cheerful HFT drill press that I got for $85 with sale and coupon.  It fit my space, budget and need for now, and for this project I didn't want to spend $60 or more on a linear scale.  I have done a number mods to it to make it better and more usable, plus added a decent keyless chuck.  Not quite a silk purse from a sows ear but getting there.

I recently added a modified HFT 4" caliper to my tail stock on the lathe and figured this might be another good application...if I could figure a way to mount it.  Here is what I came up with.

The two tricky parts of this were figuring out how to keep it tucked in close and how to attach it to the quill.  I ended up with it on the left side instead of the handle so I could touch off and set Zero using both hands.  Then there was the question of moving the gauge or the magnetic bar?  Over all it felt better to move the bar, so it ended up inverted as you see.  This does present a minor problem, in that I have to remove it to change the battery.  So far I have not had to change the battery on my tail stock version and have used it for ~3 months now and these have an auto shut off feature...fingers crossed.

The Build
I started with building the backing plate because I new that I could slip a piece of sheet metal in behind the plastic switch housing and could anchor it with the 4 screws.  First was to measure the bolt pattern and figure how much material I would need.  The two little screw holes were for ground attachments and would need to allow for those as well.  Basically I used the plastic housing and appropriate transfer punches to layout the back part of the plate and took measurements for the returns.  I did have to measure for the location of the ground screws and transferred them to the sheet metal with calipers.

I used .064 AL as I had a piece about the right size, cut it to size and drilled all the mounting screw holes.  These shows basic dimensions via the scale.  The caliper is already mounted because I never took pictures of just the plate.  If you pick on the pictures you can zoom in with CNTL +

 I ended up trimming another section out above the caliper because of the wiring, and putting a bit of electrical tape to stop any possibility of chaffing the cables.  It also required modifying the cable clamp that mounts to the bottom of the belt guard.  It was made to clamp the wires horizontally but looked long enough to flatten it out and re-bend it to hold them vertically...barely made it with a bunch of E-tape for buffer and some filing to elongate the mounting hole, as you can see below.  There is plenty of clearance, holds them snug against the casting and clear of my bracket by about 3/16" its safe and cheerfully modified.  ~¿@

Detailing the Caliper
I knew from my tail stock build these calipers need some TLC to take the cobby feel out of them so proceeded to open this one up and go through it, plan my layout and scribe some cut points on the bar.  These are pictures of all the pieces if you decide to take one all the way apart...and turned out for good reason.

First I broke off the depth tang (spot welded) and cleaned up the bottom of the channel with the Dremel, then a silicon carbide dressing stone.  Using a cut off wheel in the Dremel I cut off the excess tangs on the backing plate and magnetic bar as shown and also shortened the bar to 5.625 long for clearance to the belt cover in the zero position.  Then proceeded to dress everything I could reach, down to a medium micro mesh pad.  Drilling the two holes in the bar tang proved challenging in that I had to use a Carbide #36 bit because my Cobalt bit squealed a painful death...Tapping them 6-32 was challenging also but luckily had a Hard, German made Spiral tap and finally got them Done!

I decided to use two 6-32 button head cap screws to attach it to the plate again instead of going with 4-40's because I wanted something a little more substantial to secure it in this configuration.   Also used the same 1" center to center and centered on the back plate of the caliper, then trimmed the screws flush with the inside of the channel.  What happened next was...I put it all back together and it didn't work...Oh My!  @¿@

Tiny Tiny Torquege!

I finally fingered it out after an hour or so of futzing with it.  Turns out the Tiny, Tiny screws that hold the PWA (Printed Wire Assy) into the housing And the 4 Tiny screws that hold the housing to the channel backing plate have a torque spec to them.  The LCD on these is driven via Osmosis (Inductive) from the PWA.  I remember a video from AVE a while back about some Mitutoyo knock offs for $33 that had this "Feature".   Also of the four backing screws. one is threaded for a nutsert in the plastic and connects a ground plane via on the PWA, but the other 3 are self pay attention where the threaded one goes!  With the proximity issue on the LCD/PWA and similar issues with the magnetic bar to the PWA, it became apparent when the LCD finally came on...but gave inconsistent or randomly jumped around.  Basically by playing/futzing with the torque on these I was able to get it to work consistently and accurately.  Something I didn't run into on my Tail Stock, but it was a good learning lesson which I'm happy to pass on to the next unsuspecting soul!  ~¿@

Spindle Clamp

Next was to tackle the attachment for the spindle.  I knew it was going to be a bit tricky because I couldn't run the bar of the caliper on the center line of the spindle and would be forward some.  Also don't have tools for cutting 2.188 holes in AL plate to make a quality clamp so I had to figure out how to do it with AL sheet metal and found a hose clamp...That should do!  Sketched out a basic shape and a flat pattern with some rough numbers and started whittling and bending.  First shot, this is what came out and worked!!  Whoohoo!

Since the bar was tapped 6-32 I just needed some clearance holes and used a couple of zinc pan head Phillips (no BH's left in the bin), cut to length with a lock and flat washer.  All I did was line up the bar with it and marked it with Sharpie, center punched and drilled.  Also because my hose clamp was a bit big I trimmed off the excess to prevent blood loss in the future.   Could have used light Loctite 222 but took no chances with the battery issue looming in the background. 

Next it was time to assemble it all and see if it works¿...hopefully!  The following pictures are a couple of mounting it up.


As you can see in the top pictures it all worked out in the end, but it was a project my dad, brother and son would have laughed at spending 2 days for a 4 hour project...a family trait I think. ~¿@  Over all it works consistently and accurate enough for me (thou or 3) and no more Sharpies or tape!  Whoohoo!  It was also a good learning curve on the caliper, fit the cheap and cheerful theme ($13 w/tax) and good exercise of the brain cells that are left. ~¿@

I had a project a while back that neither Sharpie or tape worked for, using a Forstner bit to counter bore a couple of shelves for my granite surface plate stand, for 1/4-20 button heads and washers.  Forstner bits mound up piles of chips so you can't see a thing without stopping every few seconds cleaning and measuring.  I ended up going a little deep on a couple so this would have been wonderful.  And now I have it!

Hopefully the battery thing won't be a problem but if it does, I may make a couple of 6-32 knurled thumb screws for the back plate and the bar fasteners....button heads are pretty clean though!  Here is a final shot!  Note the snake light is a great tool I got from Lowes ($20) and is handy all over the shop and elsewhere...rechargeable with a spare, too!  Maybe next I'll tackle the spindle...but only the Shadow Knows!  Till Then, have fun and keep making chips...~PJ