Power draw bar

Tormach's design uses a stack of three 100mm cylinders to compress another stack of 4 pairs of opposed belville washers.









Article about duplicating the Tormach Power drawbar:

http://danielbauen.com/make/index.php/tormach-milling-machine/tormach-power-draw-bar/



SMC cylinder CQ2B100x12-3 (Tormach uses a Chinese knock-off ):

http://www.smc.eu/portal/NEW_EBP/05)Standard_Air_Cylinder/5.2)Estandard_Air_Cylinder_/g)CQ2/CQ2_EU.pdf

Alternative cylinder from Fabco:

           

http://www.eartaker.net/machining/milling/zx45.php

The cylinder used for this machine is a Fabco Multi-Power MP3x1x3x1FF

Fabco catalog for stacked cylinders:

http://www.fabco-air.com/pdf/Sec_5.pdf




However, based on Daniel Bauen's experience:

"I don't believe that a Air Piston/Bellville washer power draw bar is a good design for the TTS style tool holders. The Bellville washers allow the tool holder to be pulled out, even when providing the theoretically necessary retention force. Tightening a rigid draw bar to the correct torque provides much better retention. This leads me to believe that a torque type power draw bar would be better. I may consider replacing this draw bar in the future with a impact style power draw bar. The downside is that the hex at the top end of the draw bar tends to wear out."

I think we are back to the impact design. Which has the merit of not requiring an expensive cylinder (the harbor freight wrench can be had for $15). Additionally, the Tormach design uses a flanged nut that for the cylinder to pull against which means that there is no load on the spindle bearings. The spindle on the RF45 is not threaded, which means spindle would likely have to be modified.

Controller box IO panels

Input output panels for the steppers and the proximity sensors. First, a quick drawing based on the Bulgin connectors and the DB25 for the parallel cable to the computer. The A axis is for future use, so I made a knock-out version on a separate panel. Thinned the 3/32`aluminum slightly for the DB connector with a 1/2" end mill. Finding a mono-line font for the engraving was more challenging than I thought it would be - there aren't many good ones out there and for some reason, the scaling would get screwed up during the import of the DWG into the CAM software... 

Connectors used for the steppers and proximity sensors:


http://www.bulgin.co.uk/PDFs/Cat83_sections/Buccaneer-2010_mini.pdf

Available from Mouser.

Three positions used for the prox sensors and four for the steppers.

Not the most robust things in the world. Step on them and they break!


Shell:

Digi-Key Part Number	708-1238-ND	Price Break Unit Price Extended Price 1 7.53000 7.53 25 6.67840 166.96 50 6.16460 308.23 100 5.13710 513.71 500 4.62340 2,311.70
Quantity Available	Digi-Key Stock: 459 Can ship immediately
Manufacturer	Bulgin
Manufacturer Part Number	PX0800
Description	CONN HSNG INSERT SHELL CABLE

Male:

Digi-Key Part Number	708-1248-ND	Price Break Unit Price Extended Price 1 8.39000 8.39 25 7.71920 192.98 50 6.80760 340.38 100 5.71350 571.35 500 5.16648 2,583.24
Quantity Available	Digi-Key Stock: 181 Can ship immediately
Manufacturer	Bulgin
Manufacturer Part Number	SA3230
Description	CONN TERM INSERT 3POS PIN SCREW
Lead Free Status / RoHS Status	Lead free / RoHS Compliant

Spindle control and additional IO research

The CNC4PC board is near capacity in terms of IO. There is only one input and one output available. This makes it impossible for the moment to add the Variable Frequency Drive (VFD) for controlling a 3phase spindle motor and to add a front panel control interface for spindle, coolant pump etc.

A possible solution would be to add additional IO via ModBus over serial with or without an additional dedicated spindle control board. The ABB ACS 141 VFD requires a 0-10V control signal for speed and 12V logic for enable, direction and start/stop.

IO solutions:

http://www.henriksplace.se/pic/pic_projects/minimodbus/pic_minimodbus.html

• 4 digital inputs, opto-isolated, with LED indicator. 
• 4 digital outputs, open collector, 500mA, LED indicator, protection diode. 
• 2 analog inputs, 0-5V, 10bit resolution. 
• 1 analog output, 0-10V, 10mV resolution, 50mA drive capabillity. 
• Wide operating voltage range, 15-30V 

http://www.homanndesigns.com/store/index.php?main_page=product_info&cPath=2&products_id=4





The I/O capability of the ModIO is;
Firmware upgradeable via Serial port.

• 8 discrete inputs. Active low with internal pull-ups 
• 8 discrete outputs capable of driving relay coils 
• 2 MPG inputs that use discrete inputs 3&4 and 5&6 
• 3 Analog inputs, 0 -5v dc, 10 bit resolution 
• 1 Character LCD driver for 20x4 LCDs 
• 1 Interface for DigiSpeed controller 
• 1 Expansion bus interface for adding additional I/O modules. (to be added) 

Spindle control solutions:


http://www.cnc4pc.com/Store/osc/product_info.php?cPath=25&products_id=303

• Inputs a PWM and outputs an analog 0-10VDC.
• Has two relays that can be used to control the direction and enable and disable the drive. 
• Uses only two pins, one for PWM and one for direction. It is the presence of absence of the valid PWM signal what would start/stop the spindle. 
• Jumper to select mode of operation, US or International mode. On US mode, one relay would be used to start CW and the second one to start CCW. On International mode Relay 1 will start/stop, and Relay 2 will determine the direction of rotation. 
• Optoisolated output signals. The analog and CW/CWW signals are optically isolated, so this board can be used with drives that make grounds common with the mains that drive the VFD or motor. 
• RJ45 Connector fast installation.

_________________________________

FTDI CABLE USB RS485 WIRE END 1.8M
RS485 USB to bare wire connector for controlling the ABB 9xxx series with RS485 adaptor
DigiKey part: 768-1041-ND
$36.14