Projects 8

Tapping Attachment

I needed to tap over 200 holes for a 12x20 tooling plate for the mill, but did not want
to have to do them all by hand. I thoght about getting a Procunier Tapping Head, but
the high cost put me off. Watching the Matsura at work tap holes using the spindle
and a tension/compression holder gave me an idea. Swapping the spindle motor for
a large servo motor for positioning control was also pretty pricy. So I decided to give
the stepper motor from my 4th axis a try. It worked perfectly. I modified the 4th axis
motor mount bracket to attach the motor to the spindle head. I made a large timing
pulley to attach to the spindle shaft. The motor pulley is a .200 pitch (XL) 15 tooth and
spindle pulley is a .200 pitch (XL) 60 tooth, 4:1 ratio. I made my own 60 tooth but you
can get them at Stock Drive Products. The belt width is .375.

The tap holder is also something I made. I based it on a tension/compression holder
used by many CNC mills that can't do Rigid tapping. It is spring loaded holder that
allows a little "give" to compensate if the machine synchronization doesn't exactly
match the pitch of the specific tap being used. There are many types of tap holders
used in the industry but I opted for a simple drill chuck. Worked very well.

The program I made to get this all working together is very simple.
Basically I just need the 4th axis stepper (A Axis) to rotate 1 revolution while the Z Axis
moves down the distance of 1 thread pitch.
For example, a 3/8-16 thread would move the A axis 1 revolution and the Z axis
down .0625 inch or 16 revs per 1.0 inch.
I set the Steps Per in Mach 3 Motor Tuning for the A axis to 800. The 200 steps/rev motor
turning a 4:1 ratio spindle pulley makes the spindle turn 1 rev when the A axis is told to move 1.0 inch. To get the A axis to turn 16 revs simple requires the program to tell it to move 16.0 inches.
This is all the program needs to be to tap the 3/8-16 1 inch deep hole.

G01 A0.0 Z0.0 F50
G01 A16.0 Z-1.000
G01 A0.0 Z0.0

In theory anyway, in practice though, I had to add some chip breaking (short tap reversal)
or else the motor would bind up trying to go the full depth in one shot. (it's only a 282 oz/in)
It was just a matter of tapping down .250 in, backing off 1/8, then tapping down to .500,
backing off 1/8 etc.
For the tooling plate I just need to go down .750 total for some of the holes so this was it's program.

(16 TPI BOTTOM TAP .750 DEEP)

G01 A4.0 Z-.250 F60
G01 A3.0 Z-.1875
G01 A8.0 Z-.500
G01 A7.0 Z-.4375
G01 A12.0 Z-.75
G01 A0.0 Z0.0
M30
M2

I made a complete set of programs for each common thread pitch from 13-40 TPI. If I need to tap some more holes, I can just copy and paste the code into a program.

Very happy with the results. I made several tests with different sizes and never broke a tap or stripped a thread.
See the videos here and here.

Click thumbnail for larger view

60 Tooth Timing Pulley Blank

Tension Compression Tap Holder Shaft

Tension Compression Tap Holder

60 Tooth Timing Pulley machining 1

60 Tooth Timing Pulley machining 2

Tapping Attachment 1

Tapping Attachment 2

Tapping Attachment testing 3/8-16 1

Tapping Attachment testing 3/8-16 2

Tapping Attachment testing 1/2-13

12x20 Tooling Plate progress

12x20 Tooling Plate

Flood Coolant Enclosure

I got tired of constantly having to squirt oil on the cutters and being covered with chips, so
I finally got around to building a flood coolant enclosure. Now it's much better.
I built the base and walls from 1/2 inch plywood and 1x4 pine.
The tray measures 42 x 55 x 5. The walls are 24 inches tall. The center section that the mill sits on is built up with 2x4's and plywood for strength. I added sloped panels on either side to direct the coolant to the sink drain at the front left. To make it waterproof, I coated the entire enclosure with Herculiner Truck Bed Coating. I ordered a gallon online from 247autoparts.com. There are a few colors available but black is the cheapest at $80 gal.
It's pretty messy, smelly stuff to apply. I used a roller and paint brush for the first coat,
then used my old Wagner power painter for the second (went much faster).
It's really tough stuff when it dries, be sure to clean yourself up before it does.
I made the walls removable for maintenance. The doors are just painted wood frames with plexiglass windows.
The coolant resevoir is a tote from Walmart and the strainer is a Garden Treasures
Pond Filter from Lowes - Model: MF500 with replacement filters Model: UP750.
I used a 900 Gph pump from Surplus Center, nice and quiet and plenty of pressure.
Picked up the plumbing pieces from Lowes too and the Loc-Line components from Mcmaster.com.

Check out the Video here.