I am in the process of building a counterweight system for my x3 mill and wanted to share the info I have found.

I took the head off (this does include the gib mount) and weighed the individual pieces, but all of them together add up to:

100.9 lbs or 45.7 Kg

What about an air cyclinder with an air balance valve to give it the constant 45KG required.
Thats what I am collecting parts for. Thanks for weighing it for me!

Any problem with using a gas spring/ air shock that is mounted in the column? I guess it could be kind of hard to compress it to install. The only thing I don't like about them is their dampening characteristic when it extends (assuming a cnc conversion, could slow down upward travel speed)

A counter weight is a good idea but it adds mass

On the X3, the strut stops the head going down at least 100mm or so.
When the head is rotated, you sometimes need to remove the gas strut.
You need a special tool to keep it (the rat trap) compressed.
Using a balance cylinder will not increase the inertia much.
Where the strut is it interferes with the job you are machining quite often.
I am going to balance mine above the head, inline with CG of head assembly.

I don't think you need one that will hold the full weight of the head. That would make driving down much harder than it really needs to be.
I don't have the X3, but rather an X2 head on a fairly heavy Z axis. Fairly heavy is kind of relative actually and is only maybe 75 pounds right now. Perhaps a little more. I used a 30 pound rated gas strut.
All I really wanted was to eliminate spin down when the power was cut and to assist in raising the spindle. Mine is on a ground ball screw and linear ways though so it would spin down rather easily before. With the power off now, I can raise and lower the Z by hand equally well in either direction.
I don't think the dovetails would need any higher rating on the springs than about half the weight of the Z. Maybe even a little less.
You could rig up a pulley system on the temporary to find out what the ideal helper weight would be for your machine using barbell weights or large sinkers. Anything heavy of known weight that you could attach. Very little is needed to counter the spindown, but more is needed to assist in raising the Z.

A counter weight is a good idea but it adds mass

How big an issue is that ? Something about inertia ? Physics was never my best subject back in school, never could figure out that sliderule :)

Those struts bring back bad memories of a few hatchback cars. What kind of lifespan to expect?

Otoh counter weights would be a pita if the machine needs to be moved.

A counter weight is a good idea but it adds mass

Yes it does. But by using the counterweight, I can get close to a perfect balance between upward and downward pressure. I have a vmc that also uses a counterweight system. It's weight is stamped 900lbs. I can take one hand and push up and pull down the mill head. I don't have it running yet, but it is rated at 550 ipm. :D

Even though the mass is increased, if the system is balanced well, it will not be a problem. I would need to adjust my Mach acceleration though to compensate.

I would rather have 150lbs of perfectly balanced system vs 100lbs of downward force on the stepper.

cyclestart.....well you have good reason to be concerned about the lifespan of the gas springs. I used 2 from MSC or McMaster Carr.....anyway.....they were being used within the temperature range specified and were properly sized based on the manufacturer's recommendations and mounted as required....you know the body higher then the moving shaft...or something like that....don't have the part in front of me.......well used one season in an outdoor sheltered environment.....they lasted 9 months.

That's extremely poor lifespan for a gas strut, considering ones used to hold up the hatch in my 1990 Camry wagon with 375k miles are still operational. I was considering a gas strut for my X2. Maybe I'll scrounge one from the boneyard instead of buying a new one.

I wouldnt let a bad strut scare you off. I have used them for lots of stuff and they last years not months. Its posible Mcmaster got a faulty batch.

I bought the ones I am using from Surplus Center. They appear to be good quality. Time will tell, though.

considering ones used to hold up the hatch in my 1990 Camry wagon with 375k miles are still operational.

Our experiences are very different. Maybe it's the temperature extremes that do the automotive struts in here. -40F to 100F. The -40F being the more likely culprit. I see a lot of local hatches held up by sawed off broom handles. I do plan to test out the LMS strut.

Ok, update on the mod. I added the 100 lbs of weight to the head for a 1:1 ratio on the mill head.

I am using a Xylotex 4axis driver, with a 425oz nema 23 motor on the z axis. Previously, I was lucky to get about 10ipm out of the z axis without lost steps. Now, since I have added the counterweight, I am able to push that to 45ipm reliably. What a huge improvement.

At some point, I may add servos to this machine, but for now I am happy. Video and pics to follow in the morning. I am to tired to mess with that now.
:D

cjdavis618....any pics of the counterweight and the installation?

Was it a weight issue or a driver / power supply one? I have heard even mini-mill guys complain about the Xylotex because it limits the power supply voltage and amps to the steppers. Both can make good steppers into dogs.

ViperTX - I have wanted to get out there and actually work with it today. But I own a computer consulting firm and had to stay in the field till just now. I've been on the road since 5:00am, got to perform an hours work, then drive back. :drowning:

I will do my best to get them up in the morning, as I still have to take them. I have the enclosure built around the rear pulley system, but I can show you how I did it none the less.


Donf - I am sure it was a little of both. I had already ordered the Xylotex kits. I had ordered a 3 axis diy and a 4 axis complete. I had intended on using them to separate my Grizzly G0516 lathe mill and CNC both halves of it. Then I got the hair brained Idea that I wanted a Harbor X2 because of the r8 spindle. I bought it, then realized how small the table was on the HF version and felt like it was a toy. I then ordered this super x3 from Grizzly, they told me that it was on backorder, I canceled the order by phone. Then 3 days later my credit card was charged and the day after my mill arrived. I decided it was fate because I love the mill. I knew that since I ordered both kits with 425 oz motors, I would have plenty of power for the x and y, Wasn't sure about Z. I already had them though.

The CNC fusion kit I got for the x3 had a nema34 mount. I made an adapter insert on the lathe and then placed the motor I had on the mill. It worked as long as you like slow. I have only been able to get about 15ipm out of it at max. That was with a full step. In micro 1/8th step, I could get 10 at max.

Since I measured the weight individually, I was able to balance the mill head and counterweight within +/- 1lb. I am able to run the head up and down as fast as what I could run the z axis without the head or mount. Basically, the brackets alone, that bolt to the boxway mount will not go faster than 47ipm. This may be a resonance issue, and I will look at that soon.

While it took lots of building and work to complete this enclosure (Almost Done that is) and counterweight, I am very happy with it.

I wasn't sure how it would work, but I managed to get a way underpowered nema23 425oz motor with a way underpowered chopper drive to run that big machine at 45ipm reliably. I am some what proud of that achievement.


One thing I still need to do is set up my new workstation area for the PC. Since I have moved all of the equipment, we had a power spike today that took out my monitor and the hard drive in the PC. So it is time for me to make a few upgrades and get started on an industrial control case. I'm going to build it for 2 cnc machines on one PC. I will not use both at the same time, so that isn't a problem.

Now that I have the mill moved and 95% completed, and soon to be 100%enclosed. I will start making a 5x5 plasma table to run on the other side of the PC Controller. It will be 100% enclosed as well with outside venting.

Ok guys, here is the pics of the installation in it's various phases.

Here is the basic framework with the fiberglassing started. As well as the backing put up.
http://i5.photobucket.com/albums/y176/cjdavis618/Milling%20Machine/DSC02773.jpg
http://i5.photobucket.com/albums/y176/cjdavis618/Milling%20Machine/DSC02776.jpg

Here is the enclosure 90% finished. I still have to caulk around the corners, add my epoxied trim (runoff boards) to cover the edges of the tubs. And start building the doors and windows of the front. I figure about 3 hours to finish, then let caulk dry.
http://i5.photobucket.com/albums/y176/cjdavis618/Milling%20Machine/DSC02850.jpg

There is a space left in front of the mill and behind it, I am working out my plumbing details and cable routing. Then those will be fiberglassed in as well.

You can see in the 1st pictures that the enclosure goes all the way back to the corner. That is where the counterweight is. If you look at the last pic, you can see the mill has the cable going into the wall directly behind the head. On the other side of the panel, you will find a 4x4 support system that holds 100lbs of free-weights from a gym. Since I am using a 1:1 on the weight, I only have to move them the same amount as the head to minimize the space needed. So, both the weights and the mill head have 15" of travel up and down. At the same level as the mill base, there is a steel support that will stop the weight from hitting the floor should the cable break. So all of the underside is usable for tanks, tools and etc.

Here is the closeup of the bracket assbly. the machine screws are drilled 2" into the casting. Therefore, they ain't going anywhere. ;)
http://i5.photobucket.com/albums/y176/cjdavis618/Milling%20Machine/DSC02851.jpg

I will try and post some video of it soon. I am moving the PC stuff over tonight and wall mounting an LCD that I just picked up for the display.

Your enclose design look nice. One thing you might want to do before you complete it is, use some additional fiberglass to "wrap" all the wood. Build it up behind the panels as well and extend it forward to the edge.

Just a thought.

Smitty

Thanks,

Actually, I am covering the wood with 4mil plastic sheeting. The covering it with the caulk (Kitchen and Bath clear Silicone) on the open areas. When the enclosure is finished, the fluid shouldn't be able to get to it anyway. But I decided to take that precaution for added safety. I have everything set up (In my mind anyway) so that it will always drain away from areas that would be harmed. Even the plexiglass on the doors will extend all the way to the edge of the frame and be covered at the seams with Car weatherstrip. So I should be covered pretty well.

I will be glad to get it done, but it is to cold and dark for me to cut things out for tonight, so I will have a full day tomorrow.