[CNC Virgin]

Well, the title says it all. Just wondering whether anyone has tried to attach a long coil spring to a milling machine head and a ceiling. Although far from perfect, it seems like a quick fix for people who like making chips instead of spending most of available time sorting out numerous problems with import mills.

[Kipper]

Not something I would consider....A simple solution=yes but there's easier ways of balancing the head on a mill.

My preferred solution would be to use a fully linear spring.

[philbur]

That seems to be the OPs proposal.

Phil

My preferred solution would be to use a fully linear spring.

[RonF]

Hello from the Great White North,
A spring wouldn't be my choice .... differing tensions could be a problem.
A cheap approach I can see is a counter balanced weight around 60 lbs.
Gas struts are also a popular add-on and it does work great on my X3.
Cheers and merry X-mas to everyone and their families,
Ron

[SCzEngrgGroup]

Hello from the Great White North,
A spring wouldn't be my choice .... differing tensions could be a problem.
A cheap approach I can see is a counter balanced weight around 60 lbs.
Gas struts are also a popular add-on and it does work great on my X3.
Cheers and merry X-mas to everyone and their families,
Ron

Gas springs seem to me hard to beat. They're cheap (<$20 each), very easy to mount, very reliable, and take up very little space. You can get them in a wide variety of lengths and spring rates.

Regards,
Ray L.

[jstiltner]

A normal coil spring is not constant force, it is a linear increase, IE at the top of the column if you adjusted it to just balance, then moved the head to the bottom, it would be pulling the head upward with some force, not balanced, but if you were to say break the lead screw the head would fly back up the column. If you were to use a spring to do this you want constant force springs, think of a tape measure or clock spring, basically the same thing. In any case, I agree a gas spring, or counterbalance weight would be best.

[AviatorDave]

That seems to be the OPs proposal.

Phil

Not really, the OP said a coil spring, which is not linear. The further you stretch (or compress) a coil spring, the greater it's force.

[extrapilot]

For my SX3, I found it difficult to implement a gas spring for 2 reasons. One is- the ratio of min to max stroke ends up limiting travel (that is, the minimum height > max height/2). So, you either get too long a spring and lose -Z travel, or vice versa.

Two is, unless you use 2 (one per side), you will find that the load is asymmetric (twist moment). In theory, not a big deal, but with these mills, you can deflect the head a few thou just with mild hand force on the spindle. And, unless you have very good ways/jib on Z, you will find that, additionally, the head will twist slightly as it moves due to slop in the ways. Z is sensitive to this since the spindle is offset 8" or whatever-tiny stuff you would not worry about in X/Y is a problem in Z.

I went with a counterweight- just a bucket with 50lbs of cement and a couple of pulleys. The really nice thing about that is, you can easily add weight if need be, and by moving the mill fore/aft relative to the pulley, you can change the load plane (i.e. pull up and back, pull just up, pull up/forward). I just made a stupid little U bracket that latches onto the SX3 cover cooling holes- so I can move that fore/aft 4-5" also. Made tweaking out the details a lot easier. I tried the strut, but switched over and have had no problems. Inertia is not a concern here- you are not doing 200IPM rapids with immediate reversals on Z (I hope!)- If you use Mach, etc, just set the accel to a reasonable value and you will not miss a step. Now if I could just get the head to not twist, it would be a hell of a mill for $1200.

Hope the info helps in your decision-
Happy holidays-

[SCzEngrgGroup]

For my SX3, I found it difficult to implement a gas spring for 2 reasons. One is- the ratio of min to max stroke ends up limiting travel (that is, the minimum height > max height/2). So, you either get too long a spring and lose -Z travel, or vice versa.

Two is, unless you use 2 (one per side), you will find that the load is asymmetric (twist moment). In theory, not a big deal, but with these mills, you can deflect the head a few thou just with mild hand force on the spindle. And, unless you have very good ways/jib on Z, you will find that, additionally, the head will twist slightly as it moves due to slop in the ways. Z is sensitive to this since the spindle is offset 8" or whatever-tiny stuff you would not worry about in X/Y is a problem in Z.

I went with a counterweight- just a bucket with 50lbs of cement and a couple of pulleys. The really nice thing about that is, you can easily add weight if need be, and by moving the mill fore/aft relative to the pulley, you can change the load plane (i.e. pull up and back, pull just up, pull up/forward). I just made a stupid little U bracket that latches onto the SX3 cover cooling holes- so I can move that fore/aft 4-5" also. Made tweaking out the details a lot easier. I tried the strut, but switched over and have had no problems. Inertia is not a concern here- you are not doing 200IPM rapids with immediate reversals on Z (I hope!)- If you use Mach, etc, just set the accel to a reasonable value and you will not miss a step. Now if I could just get the head to not twist, it would be a hell of a mill for $1200.

Hope the info helps in your decision-
Happy holidays-

The simple solution to your first problem is to move the attachment point for the upper connection above the head as far as necessary to accomodate the compressed length of the spring. If that attachment is centered on the head, and, if necessary, constrained to move only vertically, the second problem is eliminated.

Regards,
Ray L.

[extrapilot]

Sure, I could have setup a gantry over the column, and run the spring vertically with a mount to the center of the head. But that requires vertical clearance, and is a lot more trouble/time than $3 in pulleys and $1 in cable. For any single side mount strut, you have asymmetric load, and raising the mount point above the head increases the torque moment via longer arm. I saw a pretty elegant solution where someone mounted up a couple of pulleys on a bracket mounted to the top of the column, and the gas spring inverted on the back of the column connected via cable. Still a little complex relative to a counterweight, but little vertical impact, and makes the mill more portable (due to reduced vertical clearance). Downside there is, makes access to the column internals a little more unfriendly, but relatively trivial. Might make for a decent little upgrade for those X3/SX3 owners on the board-

Best-

[extrapilot]

btw- at least in my case, I have found it very helpful to be able to adjust the amount of counterweight as things evolve (i.e. ways get cleaned up or jib replaced) and also just for initial tweaking. That was one challenge with the gas springs- was not sure which value was best. It would be easier to select now that I know my machine better.

[philbur]

Check the definition of linear spring.

For example:

"What is the definition of linear spring?

A type of spring designed so that the force deflecting the spring is in direct proportion to the distance the spring travels. The linear spring is the most common type of spring"

Phil

Not really, the OP said a coil spring, which is not linear. The further you stretch (or compress) a coil spring, the greater it's force.

[SCzEngrgGroup]

Check the definition of linear spring.

For example:

"What is the definition of linear spring?

A type of spring designed so that the force deflecting the spring is in direct proportion to the distance the spring travels. The linear spring is the most common type of spring"

Phil

The "ideal" common coil spring is, indeed, a linear spring, which creates a force linearly proportional to the deflection. Real springs exhibit this behavior only over a relatively limited range of deflection. Beyond that, the force per unit deflection increases. I believe the earlier reference was to a "constant force" spring, which is a different animal. This is a spring whose force is constant, regardless of deflection, which is really what you want in this application. A counter-weight will behave like a constant force spring. Any spring which is very long compared to the deflection will behave like a reasonable facsimile of a constant force spring as well. The type of springs used in mechanical watches, roll-up garage doors, gas springs, and the return spring in a common tape measure are also, approximately, constant force. All have an increasing force per unit deflection the greater the deflection, but the change in spring constant is relatively small.

Regards,
Ray L.

[DICKEYBIRD]

Here's how I did mine. I used some old auto brake discs and other scraps to get it to the correct weight. The head will move effortlessly up & down using one finger if desired. Use the vented style discs as the vents make a great place to stick your chip brush, wrenches, etc.

[Thorpydo]

In regards to those saying that a strut is a better solution than a spring because the force of the spring changes with deflection. . .

What do you think happens in a gas strut? When the strut deflects, the gas inside compresses and raises pressure and force.

I use a gas strut and it works just fine for me. My machine is CNC'ed and even before the strut was installed I didn't notice much difference.

Sure, a spring from the roof would probably work, but I think a strut or pulley system is easier.

[SCzEngrgGroup]

In regards to those saying that a strut is a better solution than a spring because the force of the spring changes with deflection. . .

What do you think happens in a gas strut? When the strut deflects, the gas inside compresses and raises pressure and force.

I use a gas strut and it works just fine for me. My machine is CNC'ed and even before the strut was installed I didn't notice much difference.

Sure, a spring from the roof would probably work, but I think a strut or pulley system is easier.

True, to an extent. The force of a gas spring is relatively constant over its travel, compared to a spring. The change is typically on the order of 10% to perhaps 30%.

Regards,
Ray L.

[AviatorDave]

Check the definition of linear spring.

For example:

"What is the definition of linear spring?

A type of spring designed so that the force deflecting the spring is in direct proportion to the distance the spring travels. The linear spring is the most common type of spring"

Phil

Yes, that is correct definition of a linear spring. But that's not what you'd want to counterbalance a milling head, which was my point. You'd want a constant force, not one that increases linearly with displacement.

A true counterbalance is the best way to do it.

[OrionBlade2003]

The coolest thing EVAR!

ZOMG!

:cheers:

I just got a Harbor Freight 3 axis mill installed in my garage, and I've got exposed bar-joist above it. made it great for rigging the mill, just took it apart and hauled it off my pickup piece by piece, then reassembled with a 65 year old chainfall.

I love my grandfather's tools. *daydreams*

Anyhow, I will definitely be hooking up something along these lines. I might put in a guide post, though, to keep the counterweight from swinging wildly when bumped or vibrated. Do you notice any problems along those lines? My milling head weighs about 150-200 pounds (it took two of us to move it, and it's roughly the smallest 1/3 of the metal in a 700 pound machine) so I'd definitely like to have a controlled-fall-zone with a rubber pad at the bottom just in case the cable/sprocket chain takes a dump on me. How much does your counterweight weigh? Is that just two disc brakes? (20ish pounds?)

*high five* on the clean install ;-)

Rion

[DICKEYBIRD]

Thanks Rion.

I don't have a scale to weigh it but I'm guessing 30-40 lbs? It's a compound pulley arrangement which doubles the effective weight of the counterweight.

I've never noticed any wild swinging motions in over 2 years of usage so I don't think that's a worry. The cable and pulleys are rated for far more weight than they'll ever see so I don't worry 'bout that either.

The only worry I had was in the quality of my weld since I don't weld very often. The pipe is an old fence post I found on the side of the road. I cleaned it up real nice and chamfered the heck out of the joint so I could get good penetration. I made the root pass, chipped off the slag and ground off any rough stuff, turned the heat up some more and laid in a decent bead. I think it's good but do check it every so often for cracks in the paint.

Should'a put in a gusset I guess.

[OrionBlade2003]

I have access to some scrap I beam, so I was just thinking I'd put that as the upright, since it's strong and rigid, and the weight could slide up and down in one of the C channels. I do have a dog now that likes to follow me around... ;-)

Totally awesome setup though. What does it really do for you, though? Is it JUST an ease of use attachment, or does it help with accuracy?