[Me...] Posted January 31, 2020 Share Posted January 31, 2020 I happened to notice something in regard to using Base Alignment Loop... No matter how your order of features are, it seems to always measure the Spatial feature first when turning on the loop. I often program my clocking feature to be measure first on a circular part that way If fixtured properly all one has to do is eyeball the locating feature on center of the probe that I have set a CMM position for. Anyone else notice this? It makes me question whether the spatial feature (Plane) should always be measured first or not... Link to comment Share on other sites More sharing options...
[Ke...] Posted January 31, 2020 Share Posted January 31, 2020 Sometimes I may have short, thin walled, cylindrical parts that I use the top plane as the spatial rotation. I will use the ID or OD of the cylinder as a reference for the circular path of the plane, using a formula. That way, it checks the diameter first, to ensure that the plane is probed properly. Link to comment Share on other sites More sharing options...
[Me...] Posted January 31, 2020 Author Share Posted January 31, 2020 I'm not sure that is related to what I'm talking about, I also happen to do that as well though. Weird flex but okay. Link to comment Share on other sites More sharing options...
[Jo...] Posted January 31, 2020 Share Posted January 31, 2020 From what I have observed. It wants to level, rotate and then any other features. Link to comment Share on other sites More sharing options...
[Th...] Posted January 31, 2020 Share Posted January 31, 2020 I feel like I saw a post by Tom Oakes or someone else recently about this. Calypso seems to follow the order that the base alignment window shows, i.e. spatial, then planar, then X/Y/Z, no matter what the actual feature order is. Edit: Found it:viewtopic.php?f=13&t=2643#p16521 Link to comment Share on other sites More sharing options...
[Ke...] Posted January 31, 2020 Share Posted January 31, 2020 RE: I'm not sure that is related to what I'm talking about Please sign in to view this quote. To clarify: Q: Should the the spatial feature ALWAYS be measured first? A: No - as sometimes other features need to be measured first, as a reference feature Sorry for the initial lack of clarity Link to comment Share on other sites More sharing options...
[Ri...] Posted January 31, 2020 Share Posted January 31, 2020 I never Loop a Base Alignment. You don't have to. A Base Alignment to me is nothing more than establishing where the part exists in the working volumetric envelope of the CMM. All my Base Alignments are as simple as they can be, no scanning just simple points, regardless of Datum requirements. Base Alignment features are never used for any characteristics. After, I have what I call a CNC Alignment which strictly uses Datum's, this is where I would use a Loop. Example: CNC Alignment1 A_B_C This way I can use what ever feature I want in the Base Alignment as my first feature. I've been using this method for about 18 years now.Untitled.jpg Link to comment Share on other sites More sharing options...
[Mi...] Posted February 1, 2020 Share Posted February 1, 2020 Please sign in to view this quote. I basically do the same thing but it may be comparing apples to oranges. With the piece parts and assemblies I usually do, my base alignment locates the part with a 3,2,1 alignment (sometimes 4,2,1). I group that as a base alignment and then I never use anything from those features again. I instead fully describe all my datums and use those in my drf's and dimension from feature to feature. In Shawns instance, I would want to set my spacial alignment first and then clock it because you get the most stability from the special alignment. It's like, picking up a box then turning it so it is right side up and then turning it to see the label. To me it's the right order. Link to comment Share on other sites More sharing options...
[SH...] Posted February 2, 2020 Share Posted February 2, 2020 Please sign in to view this quote. I feel wonder after read your post, what would happen if we used base alignment feature for characteristic, what would happen if we use base alignment feature for scanning, what is the advantages of we left base alignment feature free from other use??. In my knowledge base alignment is the platform in which we do all the operation so it should be based on primary,secondary, tertiary datums. I don't have that much experience you have , I don't know the advantages that's why asking, don't mistake me?? Link to comment Share on other sites More sharing options...
[An...] Posted February 3, 2020 Share Posted February 3, 2020 Please sign in to view this quote. Also my experience. Link to comment Share on other sites More sharing options...
[To...] Posted February 3, 2020 Share Posted February 3, 2020 In my opinion, I don't believe you can say "never use a loop". Even if the BA is a 3-2-1 alignment, and you measure the DRF features afterwards, repeatability of your results will improve with a loop on the BA, even if it without a condition statement. How close you want them to repeat, is up to you. For example, your machinist asks you to measure a part. You hand him the part and the report. He questions the results and asks you to measure it again. This time the results are slightly different. The machinist says "Which results do I use?" One of the main reasons the results are different is because the measurements were not taken in the same exact place. Sure the 3-2-1 alignment gave you a coordinate system but unless you fixture the part in the same exact orientation and location, the BA is probably not in the same exact location. Then, the features measured afterward are not in the same exact location. Then, the results could vary. If you're measuring something with +/-.005" tolerance and you get .0002" variation on a repeat measurement, maybe "who cares?"....What about +/-.0002" tolerance with .0002" variation? Would use a loop for 3d Best Fit or RPS alignment? Why? I feel it is for the same reason, though I understand the complexity of these types of alignments vs. standard geometry. Shawn, when you add a loop, the BA will run in the order of the BA Spatial > Planar > X Origin, etc. Link to comment Share on other sites More sharing options...
[Me...] Posted February 3, 2020 Author Share Posted February 3, 2020 Please sign in to view this quote. This is the EXACT reason I have a loop for the BA. We were measuring a small bore (Ø .060 - .0619 Imperial) & I looked at the initial valueA reading for the first attempt and it was a number I am not particularly satisfied with so I added the loop. This part is extremely small and the alignment is complicated due to how awkward and small it is. Link to comment Share on other sites More sharing options...
[FR...] Posted February 3, 2020 Share Posted February 3, 2020 Tom, Is there any way we can do before BA, to loop the start alignment or any other type of alignment? I mean CMM will do start alignment first (iterate the initial alignment to locate part as closer as it can), and then do a BA to set up datum reference which feature output related. All my program are start alignment - loop BA, would like to know way of loop start alignment - BA, which I used do in PCDMIS. Link to comment Share on other sites More sharing options...
[To...] Posted February 3, 2020 Share Posted February 3, 2020 Please sign in to view this quote. Not that I am aware of. Like the other people have stated, I am okay with doing a simple BA, i.e. 3-2-1, loop if desired, then measure my Datum Features as part of my program. When I select the Datum Features in my characteristics, that creates a coordinate system on its' own for the evaluation. Link to comment Share on other sites More sharing options...
[FR...] Posted February 3, 2020 Share Posted February 3, 2020 Thank you Tom! I guess I was so used to other software and think this is one of the disadvantage of Calypso, compare with other CMM software. Link to comment Share on other sites More sharing options...
[An...] Posted February 3, 2020 Share Posted February 3, 2020 Please sign in to view this quote. Honestly Tom! The results could vary within the limits of the CMM repeatability. Link to comment Share on other sites More sharing options...
[An...] Posted February 3, 2020 Share Posted February 3, 2020 Always use a loop,if the drawing shows a three,two,one datum reference system. Link to comment Share on other sites More sharing options...
[Mi...] Posted February 3, 2020 Share Posted February 3, 2020 basically what Tom said. There are some jobs that I always use a loop. Especially if the base alignment is a bit tricky. Sometimes I use a loop just to be on the safe side. Link to comment Share on other sites More sharing options...
[Jo...] Posted February 3, 2020 Share Posted February 3, 2020 Observation.. I always put a conditional loop on mine. If the part is close to size, shape , and position as the last time you ran it, no problem. It will probably meet condition statement in first or second run. If parts vary and fixturing is not rock solid it's no big deal. It will loop until condition is met. I usually only run a manual or start alignment once, the first time the part is run. Link to comment Share on other sites More sharing options...
[Cl...] Posted February 3, 2020 Share Posted February 3, 2020 I eliminate a lot of those variables by making a very solid, stable, Poke Yoke fixture attached to a specific, permanent spot on the CMM. Link to comment Share on other sites More sharing options...
[Ri...] Posted February 3, 2020 Share Posted February 3, 2020 Please sign in to view this quote. The BA will not have anything to do with the part other than describing to the software where it exists. The CNC Alignment manages everything. No feature used in my BA is allowed to be used for a characteristic. I haven't experienced result deviations from rerunning the same part, off the fixture, back on the fixture, etc. With Retract setting of .0787 (Inch) my part could be off on the fixture around .040 (Inch) and still not have a repeatability issue. For the last roughly 16 years I haven't seen an issue (Less poor fixturing). Link to comment Share on other sites More sharing options...
[To...] Posted February 4, 2020 Share Posted February 4, 2020 Please sign in to view this quote. Some folks don't have the luxury of fixtures. I was only trying point out that a loop may be necessary for some set-ups. Yes, Rick and Andreas may "never" use one, but that doesn't mean it should never be used. That's all. Link to comment Share on other sites More sharing options...
[Cl...] Posted February 4, 2020 Share Posted February 4, 2020 Please sign in to view this quote. I agree Tom. Link to comment Share on other sites More sharing options...
[Ch...] Posted February 4, 2020 Share Posted February 4, 2020 I tend to measure a lot of non-typical parts. Mostly rotational parts with no clocking features and that are not symmetrical . This is how I loop my base alignment. Link to comment Share on other sites More sharing options...
[SH...] Posted February 4, 2020 Share Posted February 4, 2020 Please sign in to view this quote. You are adding formula to the base alignment?? Link to comment Share on other sites More sharing options...
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