Power drawbar project (TTS system)

[DEVILHUNTER]

Changing tools is taking to much time to my, and nowadays time is a limited resource in my life, so I though it would be a great idea invest some of my time in a power drawbar. It will use the Tormach Tooling System, for those who don't know it, it's just a stright shank tool holder mounted in a collet in the spindle. The tool holder also has a flat ring that allows you to have Z axis repetitivity. If you want to know more about it, just google it since is becoming pretty popular in the hobby world because it's simplicity and cheapness.

The power drawbar cylinder I'm going to use is a 4 stage cylinder. This is in order to multiply the force of the cylinder. It will have around 2 tons of force, in fact I'm having problems to fing Belleville washers strong enough. The idea is to make sure I won't have any tool slipeage. My splindle is MT3 so it will clamp the shanks pretty tight.

I have designed the power drawbar to be modular. I can easily add or substract stages, or even enlarge them. It will be the floating type. Other types use a smaller one stage cylindern and multiply the force with a lever, but this applies all that force on the spindle bearings, and with a quill this is not a great idea.

The cost of the project will be around 100€, taking into account I had to spent 30€ in o-rings, while I'm only going to use less tan 20. Here you have the CAD model, with the work in progress 20 tool ATC.



Started buying lapped tube for hydraulic cylinders. 100mm ID and 110mm OD. I bought it 600mm long, although I only need around 150mm, but decided it will come handy to have it around for other projects.



After cutting the slices with the hacksaw, mounted my ER40-to-4 jaw lathe chuck in my mill and turned them to size.

[DEVILHUNTER]

Mounted my vise sideways so I can easily swap the parts, drilled and tapped the holes where the pneumatic fittings will go.



Machined a T-shape nut that will go threaded in the top of the spindle. Threadmilled it and used a small T-slot cutter to make a relieve groove for the threads.



Funny how all the chips got magnetized and kept on the tool.



Finally this si how the stack of spring washers will fit. )))((()))((()))((())). Great thing about belleville washers is that you can get whatever force and legth of travel of your spring just you want by stacking them together.

[pinstripe]

Nice. Did you consider making an electric one, or was it always going to be pneumatic? Mine is pneumatic, but I do wonder how much quieter an electric one might be.

[phil burman]

Nice. Did you consider making an electric one, or was it always going to be pneumatic? Mine is pneumatic, but I do wonder how much quieter an electric one might be.

Is such an animal available, any links please?

Phil

[DEVILHUNTER]

Always designed it to be pneumatic. Does yours works with an impact wrench? Mine should be quiet, and you can allways use a noiseless compressor. It won't use too much air, even a homemade one with a fridge compressor would be enough.

What I do though about is my mill motor. Currently I'm running the DC original motor (1.1 KW), which won't last long. I have an 1.7 KW AC servo motor that is perfect size to fit in there, even could be bigger. The problem is that I don't have the servo drive yet. I will try with a Vector VFD that is supossed to be able to run permanent magnet motors and, if it doesn't work, I would buy a 3 phase one. The 3 phase would be way bigger than the servo, and probably the power drawbar won't fit with that motor installed. In that case I would use a small hydralic cylinder conected to the power drawbar.

Well, to make the piston and intermediate plates I used a 10mm 7075 aluminium plate I had at home. It was going to be for my 4th axis but finally decided to use steel there so I can hold indicators. The plates were perfect to make two pistons and two intermediate plates each one, but I had to be carefull with the hacksaw to get the cut straight.



After the cut, I held the plate in the table, with some wood under it, with a couple of clamps on the sides.



In that position, I drilled the center and used the boring head to increase it up to 20mm snug fit. Then, without unclamping the part, I added another clamp in the center hole. After tighten this clam, I unclamped the firsts ones, now I was ready to mill the outside.



Then used the small T-slot cutter to make the o-ring groove.

[DEVILHUNTER]

Ooooooopsss!!! I made a UNI-Torx nut! While making one of the intermediate plates I didn't realized in the CAM were one of the last contours was going to start and I crashed the machine at G0 (3500 mm/min) with the clamp. Luckilly I was nearby and could stop the machine before something worse happened. Funny thing is that the cutter didn't get damaged at all.



Since the intermediate parts were going to be machined in the back too, and the clamping and unclamping of this setup was too slow, I decided to go into another aproach. Clamped my small toolmakers vise to the mill and put a piece of the 20mm chrome plated hydraulic rod vertically on it. Indicated the exact center of the rod and drilled a through hole on it. Now I can just fit a part, install a clamp on it and hit cycle start in just ten seconds. What was even greater was that the vise size was perfect, allowing me to mill the side of the parts in one setup without hitting the vise.



Decided to go ahead and blue the steel parts in a caustic salt bath. It was my first time trying and turned out great, not perfect, but great. The cylinders finish was quite black (ST52 steel), the T shaped nut (F125/4140) was kinda brown, but I really didn't bother to finish it with sandpaper before. I did finish the aluminium parts with sandpaper, also rounded the edges of the piston plates in the mill with a woodworking bit. I think the contrast between the clear aluminium and the black steel is very pretty. Also cut and chamfered the chrome plated hydraulic rods.



Checked the height of the pneumatic fittings holes were right once the intermediate plate were mounted.

[RB211]

No lathe?

[Sparky_NY]

Very nice ! I am curious what your mill is, a RF45 type?

I have a RF45 type in process of being retrofitted to cnc. I used a bought 3 stage pneumatic cylinder in the same fashion as you are, only real difference is my spindle is R8, I got the TTS R8 collet. I also have a toolchanger in mind for the future.

George

[pinstripe]

Is such an animal available, any links please?

There probably aren't many commercial units. I know there is this one http://www.grizzly.com/products/Elec...-Drawbar/H8368

Most are custom built from cordless impact drivers.

Always designed it to be pneumatic. Does yours works with an impact wrench? Mine should be quiet, and you can allways use a noiseless compressor. It won't use too much air, even a homemade one with a fridge compressor would be enough.

Yep, mine is an impact type. Most of the noise is from the impact, but the motor isn't what I would call quiet. It spins at 3,000 RPM. I do have a "silenced" compressor. Nowhere near as quiet as a fridge compressor, but pretty good.

This is an interesting project. Thanks for taking the time to post it here.

[boslab]

Ooooooopsss!!! I made a UNI-Torx nut
I had an odd expirience years ago with a NC drilling machine, it was drilling through 6mm mild steel bar for pins to be stuck through and pressed to make dog combs (I think they were for dogs but I had enough hair to use one in the 80s), the titex drill bits were breaking continually, I called the drill company and a rep came, he looked at the machine and upped the drill feed by about a factor of 10, I was horrified, started the machine, bear in mind the holes were .06 or less, I could hardly see the thing drilling, it was slamming the drill bit into the steel like a sewing machine, the drill didn't break, it lasted all day till the holes started wandering as it had got blunt.
The fact that sometimes you hit a cutter hard seems to save them, I cut through a 1/4 steel bolt yesterday with a wood circular saw, brand new blade, I thought that's buggered it, I checked it with a magnifyer, one tiny chip on one tooth, I think I ran out of lack for this week!
Nice job btw, love festo fittings myself
Mark

[John Stevenson]

I query the pressure of the cylinder and springs on a MT3 taper ?
On an MT3 it takes roughly twice the load to release as it did to tighten.

[DEVILHUNTER]

No, no lathe... yet, RB211. I can say I'm making one.

My mill is a WEISS WMD30, a bit smaller than the RF45 type, Sparky_NY. I want my ATC to be simple, just another pneumatic piston plus a stepper motor to index the tools. Point was I want the tools to be in a full step of the motor, so I can choose only 10 or 20 tools for the ATC. Luckily when I was drawing it I notice that the 20 tools one fits just perfect without hitting the column by just a few millimiters. Before knowing that I was thinking on a second ATC in the other side, or a chain type one.

The pint is that with the MT3 splindle I can't use the impact power drawbar since they have the tendency to self lock because of so small taper, pinstrip. Also mine is going to by way cheaper than that electric one!

Nice history boslab, remind me when you are starting in the machining world and you try to be so carefull with your tools that the rubbing destroy them.

That's an interesting point, Sir John. With the stack of disk springs I'm going to use, I got around 8700N of preload at 75%. My multi stack piston is 100mm in diameter, and the rods are 20mm. That gives me a bit more than 300 cm^2 of efective surface. My compressor will be set between 6 and 8 BAR, so that is 18000 to 24000 Newtons, I think that is goint to be more than enough to release the MT3.

This week should arrive the tool holders and the material for the final plates I need. The o-rings and pneumatic fitting are going to take more.

[bborr01]

When I saw the term "4 stage cylinder" I was expecting to see a cylinder with 4 different diameters that could fire independently of one another. Those look to be all the same size. It doesn't seem like having them being the same size would give you any more pull force than a single one. Or am I missing something here?

Brian

[Noitoen]

It has the same force as a cylinder with double the diameter. Think of 4 cylinders pushing the same direction at the same time.

[Sparky_NY]

Here is a link to a commercial cylinder of the type being built, for those that are not familiar with them.

http://www.fabco-air.com/products/multipower/multipower.html