2-axis Sharp knee mill revival - Now with 50% more axes!!

[FlySox]

Limit switches: I could use some advice. I just installed a switch for the X-axis, utilizing tapped holes that seem to be pretty standard on most knee mills. The Y-axis is a completely different story. Anyone care to share pics of their Y-axis limit switch setup? I don't look forward to drilling and tapping holes in my mill, so I really want to nail the design before I begin.

Here's the X-axis switch I just installed:

For some reason, I have quite the collection of mechanical switch options for Y

[FlySox]

Didn’t get any suggestions on the y-axis limit switch placement, so I just dove in blindly this weekend. I decided to put the switch on the moving part of the table and the stops on the base. The idea is to hang a L-bracket on the table base and bolt a roller plunger switch to the bottom of it. The plunger will hit ramped stops attached to the base near the end of the travel.

There was one existing tapped hole in a position I could use, so I mirrored its approximate position and got going, first with the auto-punch:

Spotting drill to keep the jobber bit from walking:

No pics of the exhausting drilling job. That cast iron is tough stuff. But finally got to the tapping step:

The vertical part of the bracket will be .500” 7075 aluminum. Saw cutting from stock I had on hand:

The horizontal piece will be .250” 6061:

I got sick of how slow the bandsaw took to cut these pieces, so I turned to a sled and table saw:

Squared up everything on the mill and cut a slot in the center of the thicker piece to nest the thinner one. Here I am tapping holes so I can bolt the two together:

Here’s the assembly with the switch on top to demonstrate its rough placement. This is all upside down from how it will hang from the mill:

I haven’t yet cut a 40 degree ramp into the stop cams, but that’s all that remains for them:

Not looking forward to drilling and tapping four more holes in the base. I might just invest in a mag base drill, since there may be quite a few more of these in my future.

[martyscncgarage]

I'm sorry, I meant to post some pictures of my Y axis switches. Many ways to skin the cat:

[FlySox]

I’ll be bolting my limit switch cam stops to my mill base this weekend. I struggled with a single hole last weekend and have four to do now where more precision in placement is required.

Any tips out there for drilling into a cast iron mill base?

[tblough]

Center punch, center drill, drill. I use 135 split point bits and it usually drills easier than brass.

[Muzzer]

I use HSSCo stubby drills in a cordless drill driver. Get into a good position so you can apply a decent force so they cut properly but be careful to avoid losing your balance / hitting something nasty if you slip or the drill breaks. Drilling perpendicularly is also pretty tricky, so I use a small set square to eye it up carefully in both axes before starting. I use the same cordless driver to tap the holes with a spiral flute machine tap, using the torque clutch to guard against bottoming out or being skew. Saves a lot of messing about and in some ways is safer than manually tapping, eg starting it cleanly at right angles.

If your A and B signals appear to have the wrong phase relationship you can swap A & B over or simply invert one of them (eg swap A and Abar over), whichever is easier. In the CNCdrive software you can check the encoder positional feedback is correct without powering the motor itself.

[FlySox]

Made a little progress this past weekend. Did some research on my style of plunger limit switch and decided to cut a 30 degree angle in my stop cams.

30_cam.jpeg (5.43 KiB) Viewed 3109 times

I cut out two small 30-60-90 triangles on my laser cutter and used them as a guide for a quick rough cut using my table saw sled.

I then used the triangles as angled parallels in the vise to clean the cuts off on the mill. The angles don’t need to be too precise, so this quick solution worked fine in this case.

Finished product:

Next step is to mount them to the Y-axis of the mill. I taped a marker to the switch in line with the roller plunger, and simply cranked the table to the extremes, marking the path of the switch along the way

I then positioned the cam stops according to the line and traced the interior slot. Auto punched, centered drilled, and then drilled the holes. I discovered why last week’s hole was so daunting: a dull, cheap bit. Got a brand new cobalt bit and the difference was night and day. I’ve made a promise to myself to no longer cheap out on drill bits. Last night, I received a beautiful Viking drill set, made in the USA, and am hopeful to be able to report better longevity with them.

Still, I did misplace one hole by an embarrassing amount, probably a tenth of an inch or so. Don’t know if the bit walked or I just punched it poorly. It will have zero effect on the switch, but it remains to be seen whether my OCD can let this slide or if I drill yet another hole. The next hole will mean the cam won’t be positioned for optimal travel within the slot. Which problem will irritate me more in the long run? Hmmm…

Here’s a shot of both cams mounted, with the switch bracket installed. The wire from the X limit switch is just temporarily running through the switch housing for measurement purposes. I’ll wire the whole thing up next weekend.

[frijoli]

Clever approach. Looking forward to seeing the finished product.

[martyscncgarage]

Is the plan to use one switch and two trippers on each axis?
If so, I think you will have to rely on using the one switch to home the machine on the far end of the travel and use soft limits on the other end.
Because, using one switch, the control will not know which end of the axis tripped and won't allow you to back off of the switch.

Marty

[FlySox]

Yes, the plan is one switch and two trippers. I don't actually have the software up and running yet, but the machine is almost fully wired now. I have X & Y switches wired in series so that only one input is used on the Acorn board. I thought that CNC12 would be able to figure out which end was tripped on a given axis based on the direction of travel, but I guess I was wrong. If I use the method you suggest, will tripping the limit at the non-home end at least stop further movement? I'm happy to use soft limits, but I like the fact that I have a mechanical switch to limit travel in case the soft limit fails for some reason (e.g. I put in a wrong value by accident).

Put a switch on the other end, tie them in series to an unused input and set it to LIMITALL. Just like you are doing with HOMEALL