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Coil Springs.

jcdammeyer

jcdammeyer

John
Premium Member
I'm in the process of building up this type of power draw bar. The air cylinder is pushed down by both the CW and CCW air to the impact wrench. Once the air is removed the project plans call for springs to return the assembly back up. ID of the springs would have to be 0.6" or so to clear 1/2" shafts. The project plans called for an air cylinder that had an internal spring but Princess Auto didn't have anything like that.

The model in the photo is exactly that. Just 3D printed parts to see how things 'feel'. Until I finish the mounting base on the mill I won't know how long to make the 1/2" polished shafts so I cut them longer for now. They are threaded 1/4-20 x 3/4" in the top and are a nice press fit in the 3D printed base. I haven't pushed the bronze bushings all the way in. The pieces will all be cast aluminium but I can't do that until we get some rain so the ground isn't so eager to catch fire with stray sparks.
 

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What set of plans do you have for such a project? And what sort of mill are you attaching it to? I think "someday" I would like such a thing on my little mill.
 
die springs might work. As I think about it, even the light ones might take too much force, hard to say, time to deploy that spring calculator. Good part is they're cheap and available in lots of sizes....kbc has a selection.

Building something like that has been on the list for while, it would be a big productivity improver. I have to figure how to do without air as I don't want to run the compressor every time I'm in the shop
 
Mcgyver said:
die springs might work. As I think about it, even the light ones might take too much force, hard to say, time to deploy that spring calculator. Good part is they're cheap and available in lots of sizes....kbc has a selection.

Building something like that has been on the list for while, it would be a big productivity improver. I have to figure how to do without air as I don't want to run the compressor every time I'm in the shop
Click to expand...
How about a cordless battery operated impact?
 
It's a House of Tools equivalent to a Grizzly G3616. The G3617 had a longer table and longer top frame so when spun 180 degrees could use the horizontal milling attachment. Mine doesn't have the hardware (spindle/motor/shaft hanger) and the X table is shorter. Just didn't have the room or the money. It did come with the pivoting table so I could eventually mock something up to do this.

I found my bag of springs last night and was able to stack a number of them to be able test against one of the two posts. The 90 PSI air has no problem pushing down the assembly against the spring. The spring pushes it up most of the way. Could be slight alignment issue. After all the mounts are still plastic. But it does give me an idea for spring size. Until I have it actually mounted and the rails at the correct length I can't buy springs anyway.

Plans for Drawbar is where I bought the plans. I bought all the bits and pieces over 10 years ago and they have been sitting in a box.

There is an interesting alternative to the impact wrench and using air. One can buy a reasonably inexpensive 50:1 planetary gear box from aliexpress and to that connect a size 23 stepper motor. Or buy it as a motor+reduction package. I used a torque wrench to tighten and loosen the TT Holder and found that this combination could provide the torque. So if you don't want air you could do it that way. Use either a second motor on a small screw to move the assembly down/up or add a leaver that you twist CW/CCW as you bring it down.

The reason I was investigating the stepper motor solution (and I may still use that) is the impact wrench spins up to a very high unloaded speed once the nut is loose. While playing, holding it by hand, I found sometimes the entire R8 + TT Holder would drop out. So on mine I'm going to mount a small magnet on the socket and a hall-effect sensor to count revolutions. It will shut off the air to the motor after 3 turns. Might only need to be 2 turns.
 
DPittman said:
How about a cordless battery operated impact?
Click to expand...

Possibly. I looked briefly at them and didn't pursue it as they all seemed to be molded plastic form factors....wouldn't work with the usuall design the way commonly used buttery wrench does- i.e. I believe you can take the back of those wrenches and there is a flat surface with tapped holes to adapt to your rig. Not to say there isn't another creative approach using an electric gun, or making the impact mechanism is also a possibility ....but it hadn't got the point I was going to put that kind of time into it.
 
Tom O said:
Why couldn’t you just use a duo action air cylinder to raise it back up?
Click to expand...
Two reasons. 1. Requires a second air valve which is more expensive, theoretically than springs and of course an extra output. 2. Without springs the tool would sink onto the spindle which means air is always required to turn the spindle.
So I'd use springs to keep the socket out of the way of the draw bar nut.
However, Princess Auto incorrectly labelled valves that are open when not powered. I do have one of those so I could use it to assist the push away from the nut to speed things up. Then springs don't need to move it. Just hold it.
 
John Conroy said:
I built a similar power draw bar a while back and I got the compressions springs at Lowes.
Click to expand...
Thanks John,
I'll check them out tomorrow. Yours look about the size I want to get. My shafts are 1/2" diameter. Did you find the linear bearings made that big a difference?
 
Awesome. One pair available at the Tillicum store and 4 at the Langford one. Just the excuse I need to also drive out to Princess Auto which is down the street from Lowes. Not sure for what but I'm sure I could walk out with something.

I've been mulling over the idea of using the extra Normally Open 12V valve. I'd still use the springs but the strength and the possible binding is no longer an issue since the cylinder has plenty of power to push it up. Then hopefully the springs hold it there even without air. And, since I want the wrench to only do max 3 revolutions for TT Holder removal compared to many more for R8 removal, driving it up might allow it to disconnect much faster.

For now I'll just use two buttons into the electronics to signal what to do. Set a max time for ON if the sensor is somehow not counting turns. And eventually I want either ModBus or CANopen from LinuxCNC to do this for me.
 
Capital Iron downtown has a large selection of springs in their hardware department. All sorts of sizes. Nuts and bolts, springs, and binding posts are all that's left of their once great hardware department.
 
I walk through Capital iron everytime I get to Victoria although it’s nothing like what they had when we were growing up. The last time I was there I tried to buy a brass casting that was made at the dockyards (Dad) I believe or Yarrows (Grandad) of a lighthouse but they wouldn’t sell it. Dad did the stained glasswork and another for my Aunt this one resides at my brothers house.
962E002E-9939-4FFD-A6D4-21995920BF58.jpeg
 
I picked up two springs at Lowes today. Cut two pieces of scrap copper tube to preload the springs. Used the upper part of the mill to hold it together since I haven't threaded the bottom of the two shafts. No point since they will be shorter when all is done.

Looks like the springs will be more than adequate.

Power Drawbar test operation.

Now to make the base that bolts to the mill head for this to bolt to. Can't move forward without that.
 
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