PM-833TV drawbar tightening solution....

[Tipton1965]

So PM sent me a wrench and a small part to attach to the spindle of my 833TV to be able to tighten the drawbar. You have to machine the flats yourself but it works just fine. I reduced the thickness of mine as well because it was too thick and stuck down slightly below the spindle. This is most likely a temporary solution for me as I'd like to add a power draw bar at some point.

 

[davidpbest]

Very interesting. Depending on your power drawbar selection/design, it probably will not need a spindle lock to function. My Maxi Torque-Rite PDB uses the guts of a pneumatic impact driver to twist the drawbar, and this impact-style drawbar tightening system doesn't require the spindle to be locked - the pounding action of the impacts cause the drawbar to turn without overcoming the inherent inertia of the spindle. Most of the other designs I've seen are based on the same impact driver concept. If you wanted to build your own, here is one of the more simple but crude designs. Of all the DIY PDB implementations I've seen, this one is my favorite (skip to 38:10 to see it in action).

If you decide to use the TTS system, they don't require as spindle lock to function either. The TTS style power drawbars simply collapse a series of Bellville washers vertically to release the collet.

 

[Tipton1965]

V. My Maxi Torque-Rite PDB uses the guts of a pneumatic impact driver to twist the drawbar, and this impact-style drawbar tightening system doesn't require the spindle to be locked

I was actually using a Rigid cordless impact gun to tighten and loosen the drawbar before. It worked quite well. I know another member here just has a small air impact wrench hanging right above his machine for this task.

 

[ahazi]

I was actually using a Rigid cordless impact gun to tighten and loosen the drawbar before. It worked quite well. I know another member here just has a small air impact wrench hanging right above his machine for this task.

I use a small Bosch impact driver with my PM833T. It works well, no need to lock the spindle even in high gear. I want something more permanent so I started to design and fabricate a system that will fit on the PM833T. The typical power drawbars that are designed for BP style head will not fit as is because there is much less space between the spindle and the motor. My design uses a pneumatic driver as I don't like the solutions with the Bellville washers. The biggest issue that needs to be addressed with a PDB is how to use the drawbar to push the R8 collet out when releasing the tension on the collet. From my experience most R8 collets need a light hit (I use a small brass hammer) to release from the spindle. I would love to hear from others about this issue. I assume that this issue of "stuck collets" is not unique to the PM833 and also shows up on other BP type mills with R8 collets.

Did anyone build a power drawbar for the PM833T? In particular one that is not based on Bellville washers and pneumatic cylinder?

Ariel

 

[Tipton1965]

I assume that this issue of "stuck collets" is not unique to the PM833 and also shows up on other BP type mills with R8 collets.

Stuck collets happened all the time with the Bridgeport mills I used when I worked as a machinist. I too have been wondering what others with PDB's do when a collet needs a love tap to give up the cutting tool.

 

[davidpbest]

The downward force on the drawbar in conjunction with the impact driver hammering on the drawbar forces the collet down and out of the spindle.

 

[ahazi]

The downward force on the drawbar in conjunction with the impact driver hammering on the drawbar forces the collet down and out of the spindle.

I need to check this out more thoroughly. With the small Bosch battery operated impact driver even when I put down pressure by hand the collet does not move out. I need to try it with the pneumatic impact driver more rigidly mounted and pushing on the draw bar and see if it will work.

I think that the commercial pneumatic devices like the Maxi Torque-Rite PDB use a pneumatic linear actuator to push the impact driver into the hex head of the draw bar and while turning left and releasing the thread it creates a downward force that pushes the collet out. This my theory from trying to understand the not very clear illustrations of these devices, I might be completely off on this.

...Of all the DIY PDB implementations I've seen, this one is my favorite (skip to 38:10 to see it in action).

David the design that you like (and I like it too) uses a pneumatic linear actuator as can be seen in the picture:

So, I am still soliciting inputs for an impact driver type power drawbar design or ideas that will work reliably with the PM833T.

Ariel

 

[davidpbest]

Ariel,

I think your decision not to implement the Belleville washer type is a good one. Those systems are not true PDB - they only push the drawbar down to release the clamping force of a TTS collet, and do not actually rotate the drawbar. I actually think of those systems as a "collet closing" setup similar to what you'd find with a 5C collet closer on a lathe. Since they don't actually rotate the drawbar, the device attached to the end of the drawbar is never released. Obviously it works with the TTS collet chuck, but makes no sense to use with varying diameter R8 collets or other R8 tooling.

I think you're going to end up designing your own PDB for the 833. Everything I've seen thus far is for use with the TTS collet chuck. I helped two friends with RF-45's implement PDB's for their machines, but of which used a butterfly-type pneumatic impact driver, and a hand lever to lower the driver onto the drawbar head and actuate the air to the driver with a rotation action.

I think you would be surprised at how little downward force is required to cause the R8 collet to be driven down/out when using a pneumatic impact driver as the rotational element. It hammers away on the hex-head and this helps to dislodge the collet. I'm not saying you don't nee ANY downward force, because you do, but it is far less than you might suspect. Whether a cordless impact driver jolting/dislodging forces are on par with a pneumatic butterfly type driver is doubtful in my mind, but who knows? In the process of coming up with these PDB's for the RF-45s, I looked at all kind of implementations.

Obviously, some form of vertical movement is required to pull the twisting device (impact driver) down onto the head of the drawbar. Lots of designs I looked at involve the operator pulling the impact driver down while simultaneously triggering the impact driver switch. This is one such design where the lever that lowers the impact driver is also used to trigger the impact driver in either direction. This video illustrates just how little downward force is required when using a pneumatic impact driver. Here's another version. This is an example (go to 29:55 to see it demonstrated) of a design where two levers are used; one to lower and lock the driver in position, another lever to toggle the impact driver either direction.

The design Colin (CompEdgeX) used I like because it is so low-profile vertically, and is activated with the press of a buttton. Yes, it does use a pneumatic linear actuator to pull the unit downward instead of pushing it from above which would double the height of the complete unit. That design originated with Stan Zinkowski at Bar Z, and he explains the use of the air cylinder and how it's configured in this video and in this addendum. Ray Canillia has a four-part video series of his implementation of this same design you can find here.

This is another (skip to 2:00) similar design but uses two pneumatic linear actuators.

The Maxi Torque-Rite and the Kurt PDBs do not use a conventional pneumatic linear actuator to move the driver up/down. The driver is contained inside a cylinder that acts as a piston inside the main housing, and air is used to push the cylinder down and a spring causes it to return. This video shows the guts of the Kurt, and the Maxi Torque-Rite uses the same method to lower the impact driver. Both the Kurt and Maxi Torque-RIte imploy a hardened splined-type head on the drawbar to improve torque and lessen the possibility of hex-head deformation.

Hope this helps.

 

[ahazi]

I think you would be surprised at how little downward force is required to cause the R8 collet to be driven down/out when using a pneumatic impact driver as the rotational element. It hammers away on the hex-head and this helps to dislodge the collet. I'm not saying you don't nee ANY downward force, because you do, but it is far less than you might suspect. Whether a cordless impact driver jolting/dislodging forces are on par with a pneumatic butterfly type driver is doubtful in my mind, but who knows? In the process of coming up with these PDB's for the RF-45s, I looked at all kind of implementations.

The Maxi Torque-Rite and the Kurt PDBs do not use a conventional pneumatic linear actuator to move the driver up/down. The driver is contained inside a cylinder that acts as a piston inside the main housing, and air is used to push the cylinder down and a spring causes it to return. This video shows the guts of the Kurt, and the Maxi Torque-Rite uses the same method to lower the impact driver. Both the Kurt and Maxi Torque-RIte imploy a hardened splined-type head on the drawbar to improve torque and lessen the possibility of hex-head deformation.

Thank you David, great information! Probably the most informative single post anywhere on the web on this topic with reference links. I scoured the web multiple times and viewed some of the above but several were new.

The PM833T is probably most similar to the RF45. Do you have any pictures of the RF45 PDB implementations?

The The Maxi Torque-Rite and the Kurt PDBs implementation is super nice with the specialized cylinder, very nice compact design with small number of components.

Ariel

 

[davidpbest]

Sorry, I was not allowed to photograph the RF-45 PDB installs for security reasons. What I can say is that they were based loosely on the version John Saunders did (first video link in previous post) with many refinements, including a high quality butterfly impact driver instead of the Horror Freight $10 POS. Seems to me that your first decision is whether you want: A) single button function, or B) don’t mind living with pulling down and holding a lever to bring the impact driver into contact with the drawbar head. Either way, you will need a regulator that doses out oil for the impact driver.