What The World's Been Waiting For - Yet Another Power Drawbar Design

[vmax549]

OH there have been many many systems over the years for R8 conversions none have survived for one reason or the other.

Heres another one

http://www.snapchange.com/r8-toolchangerproducts.htm

[kcrouch]

I think that there are lots of people representing them. I found the manufacturer though. Better pricing and the ability to work out a deal on what's included in the kit. I have used them for years and they work well if used correctly.
Kenny

[HimyKabibble]

OH there have been many many systems over the years for R8 conversions none have survived for one reason or the other.

Heres another one

http://www.snapchange.com/r8-toolchangerproducts.htm

Terry,

That one is interesting, and seemingly very simple.  Any idea what it costs?  It appears to require non-standard tool holders?

Regards,
Ray L.

[simpson36]

This seems similar to this system.
www dot mach-1tooling dot com

I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.

Kenny

This is interesting, but it is not an automatic tool changer.

[simpson36]

This seems similar to this system.
www dot mach-1tooling dot com

I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.

Kenny

Kenny,

I find that system fascinating.  The pullstud mechanism is precisely what I had in mind for a future "upgrade" to my setup, and proves that it CAN be done.  What really surprises me is the very low drawbar tension - apparently only 600#?  After my testing the last few weeks, I'm amazed that's enough to securely hold an endmill in a collet.  Do you by any chance have a means of measuring (even crudely) how much torque it takes to make a 1/2" endmill slip in a collet using that setup?  I was able to do it by clamping a vise grip on a scrap endmill, and using a $5 hardware store "fish scale" to pull on the handle, then calculate the torque based on the fishscale reading and the length of the vise grip. That would be invaluable in helping me correctly calibrate my drawbar.

I'm going to read their patents and see what I can learn....

Regards,
Ray L.

Ray, isn't this apples to Oranges? This is not an autromatic tool changer.  The 600# is not applicable to your setup. You are relying on friction alone to turn the tool. This setup is using the R8 collet which has a psitive drive. The drawbar has only to keep the toolholder in the spindle and 600# is plenty for that.

I continue to think your #2000 number is closer to the mark. I'm sure you are familiar with breakaway torque and I think the 'problem child' in a friction hold is going to be chatter, where you are going to see extraordiarily high shock loads which are powered by the inertia of the rotating mass and not by the motor HP. 

[simpson36]

Couple more thoughts:

Making a spindle from scratch:  That comment was made to Vmax who apparently has the capability to machine a spindle, and who also presented the idea of someone making a custom spindle as a product.  Many moons ago when I had my own small shop for building prototypes and specialized high strength parts, I did my own heat treating and had a tool post grinder, so like anything else, no big deal if you have the tools for it.

That said, I don't think the spindle is, or should be hardened, except perhaps case hardened to a few tens for durability. Spindles are subject to shock loads from chatter and hardened steel is not a good choice for shock loading, unless you are talking about S7, which IS expensive, is precisely hardenable to a specific depth, but you would still leave the core soft and you would still have to be stress relieved after hardening and before grinding.

I presume you can still buy pre-hardened and stress relieved machinable rounds? I used a lot of this stuff before I got my own furnace. However, I think for the purposes we are talking about here, a new spindle made from stressproof steel round with no heat treatment at all would be adequate. I would grind only the R8 taper and then only after the bearings were installed and it was in the head already. I replaced the pathetic bearings in my X2 head and then re-ground the R8 taper and I show zero runout on a .0005 reading Starret, which is more than adequate for my purposes.

Positive drive: Auto-changing an R8 is frought with challenges, but it seems to me that the Tormach setup could be easily modified for positive drive, potentially halving the tension requirement on the drawbar.

[poppabear]

Here is a Prototype I made for a Tormach......

http://video.google.com/videoplay?docid=8421475437071753563

I ended up having to double the Power of the Cyclinder and double the power of the Beviels, that allowed me to have a consistant 3/8th inch cut.........but NO deeper, things would pull out.......

This ATC has a DL06 PLC coupled to mach for the ATC control, and used Air for the Drawbar piston, and swing arm piston.

The idea works, but for it to be something I would stand behind legally, I would have to add some kind of positive locking Pull stud to the R-8 System, That would push the cost even higher......

scott

[HimyKabibble]

Here is a Prototype I made for a Tormach......

http://video.google.com/videoplay?docid=8421475437071753563

I ended up having to double the Power of the Cyclinder and double the power of the Beviels, that allowed me to have a consistant 3/8th inch cut.........but NO deeper, things would pull out.......

This ATC has a DL06 PLC coupled to mach for the ATC control, and used Air for the Drawbar piston, and swing arm piston.

The idea works, but for it to be something I would stand behind legally, I would have to add some kind of positive locking Pull stud to the R-8 System, That would push the cost even higher......

scott

Scott,

How much drawbar tension are you running?  Any pictures?

Regards,
Ray L.

[poppabear]

2,400 lbs approximatly in belviels,
Pics of the build are under the tormach thread of the cnc zone.

scott

[HimyKabibble]

2,400 lbs approximatly in belviels,
Pics of the build are under the tormach thread of the cnc zone.

scott

Scott,

So, with 2400#, you can't cut deeper than 3/8" without pull-out?  That would not do me at all....  By my calculation, I manually tighten the drawbar to about 4500#, but that seems severe overkill to me.  How have you verified that tension?  What kind of cut woudl cause pullout - what tool, RPM, feed, etc.?  I just yesterday tried a 5/8" endmill at only about 500# tension, and saw no pullout....


Regards,
Ray L.