How does accuracy effect CNC work? - Solid Modeling

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boydage		#1 Posted : Friday, August 12, 2022 3:58:18 PM(UTC)
Rank: Guest Joined: 7/9/2016(UTC) Posts: 22 Was thanked: 8 time(s) in 7 post(s)		Designing a piece of equipment that I am cutting out of 6061 Aluminum. Aligning all my components (this case linear rails), creating drilling holes for assembly. I have found that the centre-line of a series of bolt holes are centers 216.968mm apart. I dont know how this has happened. Everything south of this dimension lines up perfectly. In this case, I am using M8 bolts the part I am screwing on has 9mm holes. So as for the assembly there is no problem if I am 0.032 in or out. My question is about the CNC work. I dont think that my machine will care if its drilling a line of holes 217.000mm apart, or if its 216.968mm apart. Have I made the correct assumption? I do remember someone talking about tramming vices once there was something about discrepencys there. Probably not related. Also - like - when is SharkCad going to be able to export metric STEP files and not have them change to Imperial!?!? Far out, I think I have given them a lot of money they just dont seem to care about bugs at all huh? Pride in our product huh. Anyways please lmk thoughts about this dimension thing. Rgds

2 users thanked boydage for this useful post.		GARLIC on 8/13/2022(UTC), specktech on 12/22/2022(UTC)
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rockyroad_us		#2 Posted : Saturday, August 13, 2022 1:19:13 PM(UTC)
Rank: Senior Member Joined: 9/12/2009(UTC) Posts: 608 Location: In my place Was thanked: 59 time(s) in 51 post(s)		The accuracy is dependent on your backlash of your machine. If you know your backlash, compensate for such. The CAD software is very accurate. if you draw 100mm holes apart, it should be as such in CAM. But the machine tolerance is always a big factor. I mainly work in 4 decimals. Regarding .stp files, those are unitless. So if you are working or importing in inches, it will import in inches. Maybe someone can add more to this. I basically work in inches. I get files from all over the world and I have never had an issue. If someone drew it in metric and export, you should be able to import to either metric or imperial and the scale will be maintained. Note that there's no option to import either in inches or imperial when selecting import .stp. So if you hare working in metric is should covert to metric despite someone drew it in inches.
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2 users thanked rockyroad_us for this useful post.		GARLIC on 8/14/2022(UTC), specktech on 12/22/2022(UTC)
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UGMENTALCASE		#3 Posted : Saturday, August 13, 2022 4:07:41 PM(UTC)
Rank: Senior Member Joined: 3/21/2017(UTC) Posts: 953 Thanks: 46 times Was thanked: 321 time(s) in 213 post(s)		Everything you do on a CNC machine needs to be aligned to the machine for sure. So the vice jaws, table etc needs to be perpendicular to the spindle yes. As for programming the drilling of those holes, depending on the software you use for programming you can normally pattern the hole anyway, so just use the CAD model as a reference point.

1 user thanked UGMENTALCASE for this useful post.		specktech on 12/22/2022(UTC)
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MPSchmied		#4 Posted : Saturday, August 13, 2022 10:27:55 PM(UTC)
Rank: Guest Joined: 4/9/2017(UTC) Posts: 516 Thanks: 280 times Was thanked: 143 time(s) in 109 post(s)		Originally Posted by: rockyroad_us Regarding .stp files, those are unitless. No. The stp files are always in imperial and cad programs know this and if you work in metric, the values will be converted automatically. This mean, however it works, it is possible to find out that the file is imperial.
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2 users thanked MPSchmied for this useful post.		GARLIC on 8/14/2022(UTC), specktech on 12/22/2022(UTC)
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rockyroad_us		#5 Posted : Sunday, August 14, 2022 2:54:27 PM(UTC)
Rank: Senior Member Joined: 9/12/2009(UTC) Posts: 608 Location: In my place Was thanked: 59 time(s) in 51 post(s)		I would not know how you will get whether it was made in imperial. Like you said it gets converted. I just tried importing to my bobcad program working in metric while I drew the CAD in inches and the convertion is fine. I don't really need to know whether it was drawn in inches. It just imports correct to the units you are working.
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1 user thanked rockyroad_us for this useful post.		specktech on 12/22/2022(UTC)
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