[orcaz1]

I have one of these round column mills that I converted to CNC (stepper motors) a while back. I drive the z axis through the existing mechanism and have the backlash down to about 0.020. I find this to be unacceptable as it seems to break a lot of the smaller end mills if I push it too hard. I have seen several references in the forum that the quill spring should be reversed. I thought I would give it a try before going to ball screw z axis drive, however, when I took the spring casing off, I find a pretty hefty 1" wide spring tightly wrapped in there. I'm looking for hints as to how to unwind it out of there and more so how to get it wound back in, in reverse. Can anyone share their experience doing this and is there a purpose built tool or gadget anyone has used to accomplish this? Thanks in advance.

[TiagoSantos]

Howdy If it's anything like the RF-40/RF-45 quill spring (which I believe it will be..) you don't want to unwind the spring!

There is a small screw on the quill pinion shaft (or whatever you want to call it..) that holds the spring in place, but it should be tight. The spring has a keyhole shaped slot, so if you wiggle it the right way, it'll come off the screw. It'll take a few tries, but once you figure it out, you'll get it every time!

[109jb]

What tiago describes is just how to get the spring and spring housing off of the mill. I am one who reversed the spring which involves taking it out of the housing, flipping it over, rewinding it and putting the housing on from the other side. It works great but that spring does indeed have a lot of force. I used a piece of 2 x 6 lumber with a 3/4" hole in it and a 3/16" hole close by. I then made a shaft that mimics the shaft on the mill with the screw that engages the spring. The shaft goes through the board with the screw that engages the spring on top of the board.I then put a 3/16" pin in the other hole and put the spring on loose in the proper direction. Then wind the spring by turning the shaft from below the board with a vise grip pliers. Once wound enough to get the housing to fit, slip the housing over the spring getting the slot in the housing engaged with the bent end of the spring. It took a little futzing around because of the 3/16" pin, but I got it on there and then just let the spring unwind slowly into the housing and then remove the whole thing from the little fixture.

[TiagoSantos]

Ah, yeah I did forget to mention the actual reversing.. Although to be honest, I can't remember much about how I did it!.. 109jb's technique is probably much better than whatever it was I did, which I'm sure involved lots of swearing.

[orcaz1]

Too Late, I quit being a chicken, put the spring cup in the vice and pulled it out expecting a big sproing and spring steel flying everywhere. It didn't happen, the spring unwound to about double the size of the cup. I then used the pinion spindle and small screw to wind the spring back into the cup in reverse position. The hard part is getting the spring back onto the small screw when re-assembling in the machine. I have a DRO unit attached to the Z axis and ran a few tests. I have to say that I am disappointed with the results. While the repeatability is good the actual position where the quill stops is as much as 0.007" different from where the program says it should be. I put this down to the rough machined parts in the quill down feed mechanism. So I have ordered a small ball screw and nut and a couple of belts and will be fashioning some sort of direct drive to the quill. Thanks for your input. When ever I get it finished I'll post some pics.

[TiagoSantos]

There is a fix to the quill drive, but it's probably harder than the alternative (ballscrew mount). You can make eccentric bushings for the pinion shaft that move it against the quill's rack and reduce backlash.. But I'd still go with a ballscrew if I absolutely had to have the quill as my Z axis. Remember that the quill itself, at full travel, will probably have as much as .010" of wiggle..

[orcaz1]

I use as little quill travel as necessary when cutting, I have built a 1" diameter ground column which is fixed between brackets clamped to the top and bottom of the column. On it is a fitted lapped sliding block which is fixed to the head. This allows me to raise and lower the whole head for tool changes without losing it's position with the table. It also allows the tool to be lowered as close as possible to the work before clamping up.