DanielBauen.com

Power Draw Bar

Tormach offers a power draw bar option for $1200. After already spending a chunk of change on the machine and other accessories, I found it hard to stomach to pay another $1200 for what amounted to be an air cylinder, air valve, and some machined steel plates and hardware.Also, I design machinery with pneumatic automation, and have cylinders, valves, etc lying around just waiting to be used for a project like this.

Tormach uses a 3 stage air cylinder with a bore diameter of 100mm. The part# of their air cylinder is CQ2B100x12-3, and it's made by a company in China called XINYIPC. These cylinders are a copy of the SMC CQ2 series cylinders. Basically they've taken 3, 100mm bore by 12mm stroke air cylinders, and stacked them in series to multiply the force times 3.

I considered a few different options of making a power draw bar that would work with the TTS tooling system.

This is your basic SMC QC2 Air cylinder clone.

Looking at this cross section, it appears to me that it would not be difficult to machine a hole in the back of the cylinder, machine a groove for a seal, and sandwhich the air cylinders together.

3 Stage Cylinder Arrives!

And it's just what the engineer ordered! This is a nice looking, hefty cylinder for the price. Matches my specs, now we need to make the rest of the parts.

Machined Spindle Pully Nut

A new spindle pully nut had to be made that has a flange that the cylinder mount could grab onto when the cylinder is compressing. This elliminates any force applied to the spindle bearings.

Since these were steel parts, which I did not have a lot of expereince machining, Helton did all the machining of these parts, and I assisted and learned.

Replacing the Spindle Pulley Nut

Eccentric mounting pin

An eccentric mounting pin is used for fine tuning the position of the cylinder and cylinder mount such that it does not touch the spindle nut, and is concentric with the spindle.

So, How Does the DIY Power Draw Bar Work?

It works great, probably just like the one that Tormach sells. I wouldn't want to be without it, it's a huge time saver. However, the retention force is not good for end mills over 3/8 in, and this is a problem that has been discussed on many forums. At the recommended tension (2.5 turns of the draw bar after hand tight), it took about 95psi to release the tool. The pull out was horrible with a 1/2inch tool. I would have to go back to the original draw bar, and hand tighten in order to use a 1/2inch end mill without any pull out.

I did a few things that greatly reduced (but not totally elliminated) the pullout.

How did I reduce the pull out.

1.  I have the release pressure set pretty high, in the 120psi range. This means tightening the drawbar more than 2.5 turns
2. Ditched the Tormach TTS Collet, bought a Hardinge 3/4 R8 Collet, and ground the face down to allow clearance for the TTS Collets. This was a huge improvement in retention.
3. Added an additional bellville washer pair, so now there's a stack of 4 pairs. This increased the travel, allowing the collets to release easier under the high force.
4. Always make sure that the TTS shanks are clean, dry and free of lubricant. Keep the collet inner faces clean.

Based on this experience, I don't believe that a Air Piston/Bellville washer power draw bar is the best 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.

UC100 Motion Controller

The UC100 Motion Controller is difficult to install with Tormach's PCNC version of Mach3. I was able to install the drivers, but the PCNC Mach3 would not recognize or use the UC100.

The problem lies in the configuration file. PCNC Mach3 makes you install the Parallel Port driver and it sets this as default control device. You have to go into the configuration file, and set the UC100 as the default control device.

• Open the PCNC3 folder, usually at the location c:/PCNC3
• Find and open the xml file called PCNC1100M3-3.xml (name might be different for the 770 series) in a text editor
• Find the the line: <Control>
• Delete the code between <Control> and </Control>
• Paste the following code between <Control> and </Control> (you may have to change the version of your controller, based on the version of the driver you are using):
  <Device>UC100-CNC-motion-controller-V2.125</Device> <Default>1</Default>
• Save the .xml file
• Start PCNC Mach3, and you should see a dialog box that pops up asking you which driver to chose. Choose the UC100.

Engraved the Boston Dynamics (of Big Dog Robot fame) logo on the back of the phone of my friend who works there.  The engraving looked stunning, and it turned out bright white.  

Settings:
Speed: 150mm/s
Power: 30%

Jelly fish flames wood box.  Cigar box which was sanded, engraved, and then coated with wax/orange oil.  I only learned later that the discoloration around the engravings can easily be removed with a wet rag.  The box was made in 3 separate steps.  Engraved the top, rotate 90 degrees, engrave the right side, rotate 180 degrees, and engrave the left side.  Unfortunatly, pictures don't do it justice. It looks amazing in person.

Settings: 
Speed: 500mm/s
Power: 50% (considering that 60% appears to be max power, ~20ma, while cutting) 

 
Other side of the box.

This light was built from surplus parts I had.  A 3W Luxeon Star LED from a headlamp that I upgraded, a cheap flashlight, a heatsink with a threaded plate, and a flexible arm.

The plastic lens was scratched with a brass brush to create a diffuse light.  This reduces glare, and is not blinding if you happen to look directly into the light.

Finished the laser cutter project!  There are still a few things to add, like the exhaust blower, and air assist.  Thanks to David and Greg for help on this project.

I had a stepper motor and matching belt pulled from a surplus printer that fit the Z-axis bracket, but did not have the matching pulley.  The belt is a 1.5mm pitch, which has tiny teeth.  1.5mm pitch pulleys are also not readily available, so I modeled one in Solidworks and printed it out on my 3D printer.  I was unsure of how the teeth would resolve due to their tiny size, and the resolution of the printer.  The printed part turned out to be functional.  The teeth are rounded quite a bit, but the belt still engaged properly.

The stock air assist nozzle left a little to be desired.  Being made from a chunk of aluminum, it was heavy, and the barb fitting was straight instead of 90 degrees (which made the air assist tubing stick out too far).

The DSP laser controller has an input for the autofocus sensor.  I thought it would be handy to have the autofocus sensor integrated into the nozzle.  The nozzle shown below is the result of these design requirements.  It has a spring loaded tip.  When the table is raised, and the part touches the tip, the electrical contacts inside the tip are lost, and the DSP autofocus input is triggered.  The table then lowers a specified distance away from the tip to achieve proper focal distance.

Design Patent Application Guide: http://www.uspto.gov/patents/resources/types/designapp.jsp

Forms: http://www.uspto.gov/forms/index.jsp#startforms

Obtaining a customer number: http://www.uspto.gov/patents/process/file/efs/guidance/register.jsp

Unnoficial Design Patent Application Guide: http://inventors.about.com/od/designpatents/a/design_patent_f.htm