[bruce34rr]

I have been using my Power Draw Bar on my 770 for a couple of weeks and am having issues with TTS pullout with a 3/8" carbide endmill in 1018 steel (0.09"radial, 0.09" axial, 6000rpm, 60ipm, 0.34HP according to Machinist Toolbox). After performing all the recomendations in the Tormach white paper like using grease on the collet (and not on the inside of the collet), I have found (and the Tormach instructions state this) that I need about 25 - 30 ft-lbs (as measured by my automotive torque wrench) on heavy cuts. But with my PDB preload adjusted so the TTS still releases, the torque is only around 10 - 15 ft-lbs. SO my questions are;
1) Are people using an impact wrench to tighten the drawbar "manually" for heavy cuts? Also, looking on the internet, I only see powered torque wrenches with a minimum torque of 50 ft-lbs and most are > 100. If you use an automotive type "Impact wrench", how do you keep from overtightening since they do not have any kind of torque settings?

2) What do people with ATC do? If I spent all the money for an ATC and still had to do some of the tool changes manually I would not be happy! As the TTS is the same for the 770 as the 1100, I was hoping if it was good enough for 1.5 HP, then I would be good with my 1.0 HP machine.

3) What kind of pre-load torque have people measured on their machines with PDB?

All in all, I still really like having a PDB but frustrating if I can only use it part of the time.

Bruce

[TXFred]

What air pressure are you running to your PDB? 90 PSI is the minimum. More is better, and will let you increase the drawbar torque.

I haven't found anything about an upper limit for the system's pressure.

[bruce34rr]

I am using 100psi (using the compressor Tormach sells).

[Steve Seebold]

I use 120 PSI with my drawbar, adjusted so I have to hold the TTS holder exactly right to get it in the collet, and with a 1/2 inch end mill, the TTS holder still pulls down if I take too much cut.

My solution is to take smaller cuts at a high speed and high feed. For that I use a DuraMill WhisperKut 3 flute end mill.

I will typically take about a .030 to .050 depth of cut at 3,500 to 4,000 RPM, about .200 to .250 wide at 30 to 40 IPM on 1018 steel.

These end mills cost a little more, but believe me, they're worth it.

If you go to the DuraMill site and read the testimonials, there is one on thre from me from back in 2005.

[tikka308]

Would LOVE to see video of this! (not doubting your claim - just would really like to watch it!)

I use 120 PSI with my drawbar, adjusted so I have to hold the TTS holder exactly right to get it in the collet, and with a 1/2 inch end mill, the TTS holder still pulls down if I take too much cut.

My solution is to take smaller cuts at a high speed and high feed. For that I use a DuraMill WhisperKut 3 flute end mill.

I will typically take about a .030 to .050 depth of cut at 3,500 to 4,000 RPM, about .200 to .250 wide at 30 to 40 IPM on 1018 steel.

These end mills cost a little more, but believe me, they're worth it.

If you go to the DuraMill site and read the testimonials, there is one on thre from me from back in 2005.

[jakemestre]

Good Evening,
I own an 1100 with power drawbar and ATC. I had to dial everything in precisely for the purpose of reliability. I've never seen or operated the 770 PDB and I would call Tormach tech support with this question, but there are several things at play here. The first part of the equation is the stick-out of the tool. the longer you're hanging out the more pullout your going to experience. The second question: is everything that needs to be lubricated lubed and everything that needs to be dry dry? The last part to the equation is how quickly the piston on the air cylinder actuates. On my control box there is a little solenoid with brass mesh looking things on the bottom. The brass ports have a little screw in the bottom and by loosening or tightening the screws you'll change the speed the air is released from the air cylinder. The tighter the screw the more slowly the actuation. Say for example that the drawbar actuates slowly and you're adjusting the tension of the Belleville washers. If the drawbar hasn't fully actuated and you make the adjustment you won't get the torque. I know that when everything is well adjusted I can take a full 2hp cut without fear of a tool being pulled from the R8. Before I figured out the screws I was having some problems. Hope this helps.