For the last couple of days I've been working on Sherline mods. One of the mods I did earlier was to add some cheap Chinese scales with remote readouts to the carriage and cross slide, that was a game changer. But I learned some things about those scales that I wasn't happy with. First, they're battery powered and no AC adapter is available. My scales also do not have an Auto-Off feature. I don't know how many times I've gone down to the shop the next day only to discover I'd left the stupid things on. The most aggravating thing is that the carriage scale will periodically reset to zero.
I did some research and found out that the Shahe clone scales, which is what these are, can be sensitive to electrical noise - there's no shielding on these things. I did mention they were cheap didn't I? 'Cause I got two 8" scales for 36 bucks and change, including shipping. I am replacing them with Igaging EZ-View Plus scales which have better resolution, shielded cables, and an available AC adapter. I got a 6" scale, a 12" scale, and the AC adapter - all for about twice the price of the Shahe clones. As an added perk, Igaging actually gives you instructions on what scale functions are available and how to use them.
I was having trouble wrapping my head around what everything would look like, so I decided to 3D model it. For the last couple of days I've been modeling my Sherline's bed, the base I've got it mounted on, the carriage, the cross-slide, the new 6" scale and read-head, and the new 12" scale and read-head. I modeled the scales and read-heads as separate parts so they would work correctly in the assembly. Once I got the parts modeled it was time to start arguing with Alibre about what I can and cannot do with constraints in assembly drawings. I've learned some lessons from the other assemblies I've done about being methodical and renaming the constraints to something that will make sense to you in the future.
I added the base to the assembly and then I anchored it. I then added the Sherline bed, and used offset constraints to position it. Then I anchored it also, and deleted the constraints I broke when I anchored the parts. I added the carriage and used coincident constraints on the dovetails to keep the carriage in its' proper location. I then added an offset constraint between the carriage and the headstock end of the bed, and played with the limits until I had the carriage restricted to it's normal movement. I did the same for the cross-slide and got the carriage and cross-slide working together as they should.
Then I started adding scale bits that were just hanging out in mid-air; getting them to move like they should without breaking anything else. Once I had everything dancing about in a coordinated fashion I started designing the brackets that would connect Tab A to Slot B. This is where I'm at now.
I've still got to finish the design of the bracket that ties the cross-slide scale to the cross-slide. The cross-slide read-head is fixed and the scale moves through it. The carriage is the opposite with the scale fixed to the base and the read-head moving on it. I still have to design the brackets that will anchor the carriage scale to the base. I just noticed that I never modeled the two existing screw holes in the carriage. I'm going to use those screw holes to mount the read-head bracket. I'll need to reposition and redesign that bracket to use those screw holes. I guess I'll have to send a change order to the customer for the extra engineering time.
Don