Lapping the ways

While I have the X-axis and saddle on the workbench, I decided to lap the ways. The Y will require removing the column (which means taking the head off again!). Bob Warfield did an extensive write-up of this procedure and I am essentially following him here, although with slightly different materials. Unfortunately, since he wrote his article, IH seems to have changed hands and the information on the subject is no longer on their web site. Bob's guide here:

http://www.cnccookbook.com/CCMillCNCConversionHome.html

IH recommendation for how much:

Grit        Strokes
80           20 - 30
120         40 - 50
220         40 - 50
320         40 - 50
500         40 - 50

Start without the gibs and re-install from the 220 onward.

I found an alternative product called TimeSaver Hard Metal Lapping Compound, which unlike the (more commonly used?) alumina grit, wont embed itself into the metal and degrades over time, so even any remnants in difficult to clean corners that make their way between the bearing surfaces wont continue to abrade them.

http://www.newmantools.ca/lapping/time.htm

Before:

And after:

Y and Z still to do, but I couldn't resist putting everything together first to see how the X&Y respond under power and perhaps to make some first chips. 

To reload or not to reload?

The X-axis screw is the least smooth of the two that I purchased used. It is a manufactured by a Korean company called Mirae. Technical details from their site were next to non-existent. There was just enough information to determine whether the part was suitable for the task - i.e. that it was pre-loaded and had C5 accuracy. There are no obvious signs of wear to my untrained eye when I examined the groove with a loupe, so my suspicion falls on the balls - which get the most wear. Replacing them seems to be one of those voodoo tasks with some folks insisting that it can only be done by the manufacturer, and others saying "heck, I've done hundreds..." I think I will wait to see how the axis does once it is in place before I embark on this particular tasks. So, for future reference:



Good threads on the subject on Practical Machinist:

http://www.practicalmachinist.com/vb/general/advice-sought-ballscrew-replacement-ball-size-184584/
http://www.cnczone.com/forums/general_metal_working_machines/7416-re-loading_ballscrews.html
http://www.practicalmachinist.com/vb/general/ball-screw-installation-question-141922/
http://www.practicalmachinist.com/vb/general/how-get-balls-back-ballscrew-nut-214577/

The gist:
- There may be two sizes of balls in the tracks. One that contacts the groove followed by a spacer ball to keep the driven ones apart. Diameter difference is ~5 microns.
-
- Replacing the existing ones with (ever-so) slightly larger balls may deal with (some) backlash due to wear, but sounds to me like a poor idea as wear on the screw is likely to be in the middle, not evenly distributed over the length.
- When reloading, keep the balls out of the "no-ball" zone between the circuits.
- For ball-nuts with external returns such as mine, use the little red straw that comes with cans of WD40 to tamp the balls down into the circuit - pity I've lost all of mine!
- Work over a (clean!!) tray to catch any balls you may drop. Ummm, well yes.
- Have the patience of a saint.

This screw is metric so McMaster is a no-go for getting the balls.
The best source seems to be:

http://www.precisionballs.com/inventory/August/Ball_0001_mm.htm

Using the mill to mill the mill

The installation of a one-shot oiling system requires distribution grooves be cut into the saddle and the head ways. Unlike Bob Warfield at http://www.cnccookbook.com/ (font of wisdom to whom I am massively indebted for his encyclopedic blog), I don't happen to have a second mill handy to modify the first one with. The problem then, is how do you modify the machine that you need to use to modify the machine? Thanks to a little inspiration from this guy http://woodgears.ca/, I decided to make temporary replacements for the saddle and the head-slide out of birch plywood. I do have a small and thoroughly crappy XY table which I bought for a hundred and fifty bucks or so way back before I got the RF so the saddle replacement doesn't have to be functional. A couple of F clamps serve to hold it in place while the second half of the dovetail gets screwed on and then the same clamps act to lock everything in place against the ways. The absolutely fabulous Glacern 6" vice, definitely many cuts above the quality of the rest of my collection of heavy things, is another of Mr Warfield's recommendations. It weighs considerably more than the XY table and altogether this setup, for cross-drilling the saddle for the oil feed, borders on the ridiculous. 

Given the lack of rigidity in the setup I take things gently: it takes three passes at 20 thou per cut with a 1/8" ball nose end mill to make each groove, blowing away the dust with air to keep the cutter free. The recommended feed rate for the cut was something like 2 ipm, very, very slow.... if only I had a cnc machine! Note the ultra-professional tin foil way covers!

Then it is time to take off the head. I'm lucky enough to have a hoisting point for chain blocks in my shop. The rigging is something you want to make sure you get right as the head weighs near 400lbs and is dangerously un-balanced because of the motor. I'm using retired climbing gear. It really would be nice to have some proper eye-bolts in the head.

I needed the temporary head-slide to be functional so I assembled everything to fit closely and then used a couple of long 3/8" machine screws with nuts press-fit into holes drilled into the plywood. These, along with the original jib locks (short lengths of rod cut square on one end and at 60 degrees on the other) tighten down the jib and hold the head in place. 

After a while I got tired of holding the air and rigged up a magnectic base to hold some pneumatic hose with a needle valve to control the flow. That leaves two hands free for the wheels.

Blurry photo, but its all done. In retrospect, I guess it would have been marginally better to cut the long grooves on the diagonal to optimize the oil distribution on the ways. 

X axis test fit

With the Y axis under control, it is time to turn my attention back to the X axis - by far the most challenging part of the conversion. For reasons that will become clear and for now at least, the ball-nut is being attached to the side of the saddle (as opposed to the horizontal surface where the original lead-nut is located). As a result, its flange (which is hardend and would therefore put up some stiff resistance to modification) will be backwards with respect to the mounting plate. This means that a little finessing is required to hook the nut up to the one-shot oiling system. The plate is cross-drilled and an o-ring fitted where the grease nipple will arrive.

I cut the end off the grease fitting on the lathe (firing the ball bearing and the spring across the shop - never to be found again) leaving a conical section for a good fit against the o-ring. A little 1/8" soft copper tubing fits nicely inside the 1/4" pneumatic tubing that will be used for the plumbing.

Here is the assembly, seen from the free support bearing end. This whole setup is slightly sketchy at best and possibly downright ghetto at worst, but I'm making the best of a difficult situation here. First, the ball-nut has to be where it is because there is no way it will fit between the saddle and the table. The only type of ball-nut that will fit is the flange-less type more typical of U.S. fabricators. However, even that type won't fit in a 1" screw. So I would be forced to use a 3/4" screw which is nigh impossible to find used or surplus on ebay in the required length. Why is this? Because the slenderness ratio i.e. the diameter/length of the screw is inadequate to meet the specifications of the machines from whence these screws come; under compression loading, the screw will have a tendency to buckle. From the research that I have done, the conversion kits that are out there for the RF 45 and clones all have 3/4" screws with a fixed / free bearing support configuration - which is the least robust for buckling and substantially lowers the rpm limit for the screw rotation. Finding a used / surplus, ground (as opposed to rolled), 0.2" pitch, 1" major diameter, C5 accuracy ball-screw with a pre-loaded, G0 (zero backlash) ball-nut (the minimum specification recommended for machining metal) with 39" of travel is entirely possible. Plus, at ten cents on the dollar, It will be significantly cheaper than a new C7 grade, rolled 3/4" screw. I purchased all three screws, one surplus, two used (which came with bearings) for roughly the same as a single new C7 rolled screw without bearings. The risk I am taking is that the used screws may be of somewhat dubious origin. They may have come out of a surplus machine - or they may have been swapped out because they are worn. I have no way to know until they are installed and can be tested under load.

Another ever-so-slightly-less-than-ideal design detail here is the mounting setup for the free support (that is, the bearing that restrains the screw radially but not axially, allowing for heat expansion of the metal in the long axis). In an ideal world, the screw would come right from the fabricator cut to exactly the right length for the table. But it don't and it ain't respectively. I am therefore faced with the choice of either shortening the screw and cutting a new journal, or creating an extension for the table. The former, despite the encouraging words on the subject from the seemingly undeterrable www.5bears.com on his epic cnc-mill-from-scratch write-up, leaves my inner machinist cowering in fear under the lathe. The latter seemed like the better choice for the likes of me-who-will-live-to-fight-again-another-day. Despite the use of mic 6 tooling plate for the mounting plates, the extension will inevitably introduce additional out-of-square error to the surface onto which the bearing is fixed. Imho, however, this kind of error is easier to correct than a home-cut journal that is a few tenths too small for its bearing!

Last and not least: skeuomorph of the day comes from my favorite hardware store, HarSupCo in Montreal: faux-wood patterned cardboard tubes.

Last parts and test fitting

All of the mounting plates for the X and the Y are done.

X:

Y:

Finishing up the last standoffs with a quick polish on the lathe.

Then I'm ready to take the machine apart again in order to test-fit the axes. The first time I disassembled the X&Y I made the mistake of taking the lead-nut off the saddle. The two lead-screw journals are held in place with bearing plates that are pinned into position on the ends of the table. This means the lead-nut has to be positioned and then fastened to the saddle after everything else has been reassembled. This would be fine, except that there is no room for tools, let alone hands, in the space between the table and the saddle! Tightening it down involved tweezers, flashlights, electrical tape, elastic bands, custom wrenches and copious cursing. This time, having learnt my lesson, I manually thread the screw off the nut just in case I need to put the machine back together to modify or remake a part. 

Y axis in place! Bolt torquing order is important in order to minimize misalignment and consequential wear. First, the ball-nut is tightened to the ball-nut mount and threaded onto the screw. That assembly is fastened to the saddle just enough to take out play but still to allow movement. The gib is reinstalled. Then the fixed journal bearing is fastened to its mounting plate and fitted to the screw, they are fixed to the base casting and the saddle moved to the closest point in its travel to the motor. Finally, now that everything is where it wants to be, the saddle to ball-nut connection can be fully tightened. The hole at the back of the base needed a little bit of extra clearance which was accomplished with a round file and a die grinder (we won't go into why there is a sawzall on the ground beside the mill in this photo...).

Y axis ballscrew mods

Like an episode of Breaking Bad, we join the action without any of the backstory. Unlike that fine example of episodic television, we may or may not understand what went on here by the end of these posts...

Given that the second-hand/surplus ballscrews that I found are worth considerably more than the mill itself, I decided to make a hole in the base casting to allow the Y axis ball screw to hang out under the column instead of cutting the excess length off the screw. Dry cutting the casting with a hole saw here as there is silicon in the cast iron. A precision machining operation! Slow going but you get there with some persistence and elbow grease.

Same thing for the front of the base casting:

I had to move the whole axis down to make enough clearance for the flange of the ballscrew. If I got the math and the measurement correct there should be about 30-40 thou to spare.

I also had to take the ballnut off the screw in order to assemble the axis. So I whipped up a quick ball keeper on the lathe out of some acetal rod. Finished diameter is a couple of thou under the minor diameter of the screw.

The keeper fits tight on the screw journal - then just unscrew the nut right on to it.

Most of the fabrication for the conversion consists of machining (rather tedious) bolt circles for the support and motor mounting plates. 

The Y-axis ballnut mount is a bit more complicated.

 Chucking rectangular stock in a 4-jaw - good video here: http://www.youtube.com/watch?v=a7HhppYHwig&feature=youtu.be

Finished part. Precision isn't astounding, possibly a few thou off, but then it doesn't need to be...

Now I just need some 3/4" rod stock to finish up the stand-offs for the X and Y axes.

First post

Small things I have made

A record of small things and a repository for the research required to make them.
Intended as a small token of thanks to all those who take the time to share their knowledge.