I love a good, simple machining fixture that can save time & ensure accuracy & repeatability. Case in point is this simple fixed vise jaw I machined from Lexan to hold a small part for machining an angle on one of the edges. Small batch of 16 parts.
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Do you zero the first part, then rely on the Lexan fixture to hold the remaining 15 parts in the correct position? I ask because I am slowly getting my ATC build up and running, and just started to familiarize myself with my probe and work offsets.
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Hi Tom,
Yes, that is correct. Hereās the CAD behind the setup. The green vertical line in the center of the part represents the edge as cut in the initial profile. The red line represents the finished surface. The other angled lines (thereās 2, separated by .005" [0.13mm] ) which are offset .118" [3.0mm] from the red line. The farthest line is the rough cut, while the closer line is the finish cut. I simply run a program end-to-end of the 2 lines, a rough program and a finish program. The rough program takes .060" [1.5mm] deep passes, and the finish program runs the full depth of .625" [15.88mm] to finish the angle cut.
There were 2 parts, the one shown and a mirror-opposite part. Same setup & fixture zero location for both, I just created mirror opposite programs to run the 2nd batch.
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Thank you for taking the time to explain that - I appreciate it. I can certainly see where the time up front to create the fixture saves time in the end.
My only concern is the angle ā¦ it looks more like 26.568 degrees to me 
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Youāre very welcome Tom, anytime for a 1F bud! 
Tsk, tsk, Tom. Better have those eyes calibrated! Reading .003 deg. heavy! 
On a more serious note, Iād appreciate drawing on your experience.
If I remember correctly, you do not use homing switches/sensors?
For the work you shared above, do you probe the first part, once it is firmly in the fixture to set your zeros? Then do you rely on the precision of the setup for milling subsequent parts?
Correct in that I donāt use homing switches. That said, I still have 100% confidence in a repeatable X-Y homing process by use of my X-Y hard stops. I only have one coordinate zero (G56) which dimensionally relates to home position. In my case, there are 3 reasons for homing:
- By requirement of the Acorn controller (well, really the software)
- To validate the soft limits
- For reference to G56, as well as other coordinates I may want to refer back to
My G56 is typically used with one of my 3 coaster fixtures. On some occasions, I donāt even do an accurate home, I just jog the machine close to home & set it, just to make the software happy.
In the case of the above fixture, I actually zeroed on the fixture pocket itself rather than the part because it was just easier to do it that way. With the non-movable fixture in place, I can confidently reload parts and be assured good repeatability.
I most generally zero in the center of my parts. Occasionally, as in the first process of the above job, I just set zero at the lower-right corner (for no specific reason) to cut out the part profiles. This zero was re-usable in a sense because I had a visual orientation of where to stick down the 6" x 6" polycarbonate sheet onto my 6" x 6" self-stick flooring piece that was stuck down to my table as a low-profile āwasteboardā. Obviously in this scenario, it was not important or necessary to be dead-accurate in placement of the polycarbonate plates, only that the 8 parts would fit on the plate. Most times my program zero is just some arbitrary zero point set once the part is on the table, with no immediate concern of where it relates to home position.
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Hey Bill,
do you do without constant dust extraction? Is the chip load and the amount of dust always low enough in your work?
Thank you for that information.
I imagine that for many CNCers/machinists there will be quite a lot of variability in what is required for their particular use case/job with respect to things like homing, work offsets, use of fixtures/work holding, required precision level, accuracy, etc ā¦
Right now I am slowly fine tuning my machine parameters for my new ATC set up.
I am trying to work slowly and methodically as I go, and I will share some of my data/results for things like spindle run-out, probe concentricity, homing precision/repeatability, axis calibration, etc in a future update - for those who like data 
For a set-up like mine, homing repeatability will be important as I will have an auto tool setter and tool rack positions that need to be found and navigated with fair precision. Having the soft limits keep the spindle away from the tool rack at the back will be another use for setting the machine coordinates through homing. I anticipate defining the G54-G59 work offsets to be a real time saver, especially for fixtures for wood projects where hitting the āgo to work originā will get me to the same zero on piece after piece.
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Yes, couldnāt have said it better myself Tom. Every user will have variability in their requirements of homing & work offsets. Buy you bring up an interesting point about ATC. You couldnāt get away with āhalf-assā homing like I occasionally do, if you hope to use the ATC functionality. Canāt wait to see more in-depth posts about the ATC setup.
@Aiph5u Yes, the types of materials I carve tend to create more āchipsā than actual ādustā. Thatās one of the reasons I generally donāt do wood. My shop is so small that I donāt have the room for the auxiliary woodworking equipment (including dust collector). That, and the fact that I like to always see exactly whatās going on with my carves @ the tip of the cutter.
My shop is only 8ā x 12ā [243cm x 365cm], which is suitable for the type of work I like to do.
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Hey Bill,
thank you for providing the metric values, much appreciated 
I had seen some images of exterior and interior you showed before, I like it because you accomodate with limited space but you seem to have everything in it.
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Just for you my friend!
You know, as someone who has grown up in the āImperialā system of measure, I really started getting a deeper appreciation for metric when I first got my X-Carve and started to modify it. Everything is metric based, so rather than fight it and convert everything to inch, I just worked with metric values and learned to embrace it. Makes so much more sense than working in inches. Unfortunately at work, everything is based on imperial measurements (raw stock size, screw sizes, etc.). I did work with metric as the primary unit of measure when I worked at Toyota 2006 - 2012.
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I will have updates soon for sure for anyone interested.
As an aside, in my efforts to dial in the accuracy of my axes, I am putting my new probe to work.
I have one of my 25 50 75 blocks (l prefer metric) in my fixture plate vice, and am probing the long side while keeping track of values in my work offset table. I do three trials to see how far from the 75 mm the values are and take the average. Then I use this to calculate the new adjusted Distance Per Revolution then update the axis. I was not far out originally, but now I am within about .01 mm. Granted, it is just over a 75 mm distance, but my hope is it will be just as accurate as my āmeasure between the two pin holeā method 
I have a 60 cm precision ruler arriving tomorrow, and I will use it as well to see check the accuracy over a greater distance (which unfortunately relies on my eyes finding the holes and marked ruler increments). I thought as well I could use my digital calipers as well with this technique, albeit over a shorter (~15 cm) distance.
Letās hope it is not all a mute point once I quantify the backlash on the axes
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Before I got certified to be an Xometry partner, I had ordered a 10" āB Gradeā standard block that I was going to use to calibrate my machine over 10". It never came (out of stock, apparently) so I ended up using (2) 1 2 3 blocks end-to-end and calibrating over 6". As I recall, I didnāt have to tweak the settings at all. Factory default values were dead-on (and mathematically, why shouldnāt they be?). For whatever reason, outside profile cuts are spot-on when I do a finish pass, but holes are typically slightly less than 0.1mm undersize, which I usually deal with by fudging the actual cutter size.
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Lol!
I enjoy thinking of the time when we will have retrofit glass scale linear encoders to our machines and be finally satisfied 
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I remember a while back when your parts were accepted by Xometry, and thinking that bodes well for the 1F and my plans for it. Albeit a slighter larger size, my hope is to get the same accuracy and precision from it as you have, at least to the best of my ability and measuring instruments.
I really am looking forward to making parts. Not so much worried about the wood projects I have in mind, as I feel they will be inherently more forgiving the the aluminum work I wish to accomplish.
I imagine you needed to prove some fairly tight and repeatable tolerances for Xometry approval.
Well, in the case of the test part it was demonstrating you could hold +/- 0.005" [0.13mm]. The exception to this was the very tight tolerance on the (2) 0.062" [1.575mm], which I purchased a reamer to do these holes with. I bought $44 worth of misc. tooling to do this job, which in addition to being accepted as a partner, they paid $100 for. They sent enough material to do 2 parts (which I did).
I have a very restrictive job filter set up, so whatever makes it past the filter I can at least look at & consider. I think this current job Iām doing is #13, and Iāve been a partner for just less than 1 year. I only take on what Iām absolutely sure I can do without problem.
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That is a smart way of doing it. I can only imagine the variety of projects that make it your way, and through that platform in general. Must be interesting work.
Well, a lot of it is pretty interesting (compared to my day job, lol). But you can really tell that a lot of the parts are designed by very inexperienced designers. Iāve seen parts that arenāt even producible on a 5-axis machine. Many would be candidates for 3D printing, but theyāre not tagged as such. There doesnāt seem to be any DFM review on these parts, which I squarely place the blame on Xometry for these parts even making it to the job board. On jobs Iāve done in the past, Iāve started contacting the customer directly (once I have their name & shipping address) with one of my coasters and a note inviting them to contact me directly if they were happy with the parts I made for them thru Xometry.
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Over the past 2 weeks Iāve added proximity sensors for homing on the X and Y axis (still working on Z but need some more downtime) and I have been pleasantly surprised on the repeatability and accuracy they have provided to the homing cycle and using that as the basis for work offsets. I have both a metric digital dial indicator and a imperial mechanical dial indicator and through 50+ homing sequence tests with controller reboots between some the error is immeasurable on my indicators .005mm and .0008" resolution respectively although you can estimate the dial indicator to .0002". I was hoping to hold .003" on homing but it has proven to be far more repeatable than expected.
For backlash testing using the same equipment I have observed 0.000mm or 0.005mm, on a machine with about 1200 hours on it (Journeyman upgrade X axis is closer to 500 hours)
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