Part II:
BT30 conversion with pnuematic drawbar
Here is a business end shot between stock R8 spindle and and the BT30:
Industrial Hobbies said they have over a 100 30 taper spindles and I can confirm they fit the PM45m mill.
To convert the manual draw bar to pneumatic you have to work within the stock spindle measurements . The drawbar hole diameter is .684" with the top of the cone at .703 for a short bit. That is because it is NMTB 30. My plan is to cut a relief above the cone where the stud would sit so my gripper can release when the drawbar is pushed forward and put a triple valve spring on top of the the drawbar in place of bellevilles. Because my motor is so large, the air cylinder will be mounted upside down in front of the head and push up on a pivot arm to push down on the drawbar to release.
I took the IH NMTB 30 spindle and bored the straight section deeper by an inch while keeping the diameter to 0.72". This allows me to fit a ball type gripper where the straight section would be. Next I cut groove a 0.25" wide and a depth of 0.95". When the grippers balls are aligned with the groove, the larger diameter allows the pull stud to be released. I made an aluminum version of the spindle and it released properly. The trick is measuring everything right.
I will post some more detail later but here are some pics of the new drawbar. It is O1 steel, properly hardened and tempered to around 55 rc. (PID kiln)
Gripper Close up:
Gripper on drawbar with bt30 toolholder:
Gripper parts:
There is no room for springs inside the IH nmtb spindle, I am putting the spring on the top of the pulley with a top hat and fabco 2 stage 4" cylinder- 1500 lbs of spindle clamping force.
Meanwhile, took 8"x 3" thick diameter round of 7075. This is inspiring me to make a new head assembly with an extension. I already cut the top plate by the y axis to the vertical wall of the base and that freed up a lot of travel. Adding an extension
Having a head extension allows up to 12" y axis travel on the RF45 type mills.
Finished part bored for (4) 5/8" bolts:
Back to the spindle, I took the plunge literally and cut the inside of the spindle to make way for the pull stud gripper. This entailed slightly boring past where the taper terminates and then cutting an internal groove for the balls in the gripper to drop into. I test fit and with the balls in place, tool holders are held and then if you allow the drawbar to move down approximately 1/2", the tool is released.
I spent some time further test fitting the spindle. I found I was .0006 too narrow when the gripper was retracted with all 4 balls in. During my initial test fitting, I only put 2 balls in. With all 4 in and the gripper assembly retracted, the tool holder wouldn't retract all the way into the spindle. As a result, I had to slightly enlarge the bore in the spindle. After that, the gripper works smoothly.
Here are a few pics:
Inside the spindle:
Tail end:
Basically you need to machine the part in the oval, make a gripper and draw bar.
After finishing the plate for the 2 stage air cylinder, I took some cuts. I put a tool in, fully inserted it using the gripper with the balls and then manually tightened the bolt on top of belville washers with a wrench. No problem taking .2" cut with a glacern 4" face mill- it holds just fine.
The power draw bar works. I am really happy because bt30 tooling is plentiful and cheap
Video below:
I cleaned up everything with the enclosure and things are starting to come together. A few pics of the mill in it's current state with a power drawbar, one shot oiler, enclosure and diy fog buster with pressurized coolant:
Shot of the mill head with the
bt30 power drawbar installed:
Belleville springs:
Overview shot showing the enclosure. You can also kind of see the 3.5" head extension.
I am getting a full 12.75" of Y travel now. I will need to make a fixture plate to take full advantage. Considering these mills have 8" of y travel, this is really awesome:
Power drawbar switch. I ended up using a foot pedal momentary pneumatic switch. Seems more robust than the toggle type and the price is right:
Diy fog buster built out of scrap 1/8" npt plumbing parts I had around and a mig nozzle tip. I forgot to snap a pic of the pressurized coolant tank but it is a whole house water filter housing modified with a pick up tube. compressed air goes in and forces the coolant out through the pick up tube connected to the top. The needle valves allow for both pressure and fluid level adjustments. Works really well:
Sample part being machined:
Thanks for looking...