Thursday, November 22, 2012

Sherline Mill - Double wide T slot clamps

I have found that with so many of my larger milling projects that clamping the maximum area is preferred especially when using 12 lb foam. Another issue is that the exact center of my Y travel is located at the front edge of the cross slide which means that these bigger millings always overhang.

I especially do not like the extra step of bonding  the blank to yet another piece of material just to have to chisel it off later.

I decided to make a gang clamp that would combine both of the standard Allen screws onto one bar giving me maximum surface area and extending a little way over the edge for added stability.

The question was how wide is wide? The T slides are 1.5" apart so right off it became at least 3", the T slot to the edge is .615" so add them up and you have 4.230" total.

I took 5/8 x 1 C channel and cut off one leg; a perfect 3/8 height without any further work.

I made V2 of the double wides out of 1 x 1 x .12 aluminum channel.

The goal this time was to get a deeper bite onto the tooling foam groove that I cut using my biscuit joiner.

Monday, November 12, 2012

Sherline CNC - Y axis cover

The Y axis components are very exposed, I had been trying to figure out an easy way to to cover them but always came back to the bellows. Not wishing to fabricate them from scratch I procrastinated.

Last weekend I found the answer in the basement of one of our local estate sales... the bellows from an old camera or developing machine. For $3 I picked up the full bellows, a little wider than a perfect fit but I think it looks OK.

The neat thing about the bellows is that it came with end plates and there are enough sides to make both front and rear covers. This picture shows both my camera bellows and my thin acetate front cover too.

I'll get the front cover converted to the bellows ASAP.

Sherline CNC - Setting Backlash in Mach 3

The machinists obsession with backlash is understandable and I have a healthy respect for having it set correctly on Mach 3.

I think 0 backlash is a little crazy, it can't realistically be done or is at least is not worth the effort, especially when it's not necessary. I also believe that my Sherline doesn't like low numeric backlash numbers at all, the Sherline wasn't made for it and would require expensive upgrades to do it right. It also doesn't like the ways too tight either.

 Two images take you through the Mach3 menus.
1st select Backlash from the Config drop down.

2nd: Enter in the numbers you get from your machine backlash analysis

Say OK and that's it.  I have set the Backlash speed to 25% after becoming very leery of running my machine anywhere near top speed. 

To get my backlash numbers I use the following method.

I set up a 0.200" travel indicator especially for quick and easy use.and developed the universal bracket that can be turned 90deg. or positioned anyway that works best.

Small detail; because the indicator is offset from the spindle it rotates and so the spindle must be held fixed. I made the little snubber you can see on the top that I can jam against the pulley to keep the indicator from moving.

Instead of the short travel indicators the long travel makes all the difference; I drive it at least 0.500" into a right angle plate and use the 0.100" jog mode on Mach 3 to go back & forth. I do it all real time; check the reading on the indicator, change the setting in Mach 3, hit enter and check the indicator again. 

Doing this once a year is not enough, I'm trying to do it at the start of every new project and I'm keeping a log too.