Setting cutter comps to virtual (imaginary) point is commonly done and allows cutting the first part to within a few 0.001" of the programmed size. We have a guy running a mill that often does setups resulting in a good first part with location and size tolerances of 0.0005". Just setting work coordinates with an edge finder or by indicating on a hole or shaft, the tools are measured up offline and the tool comps set and the program run. But then we have another guy who will always have oversize chamfers on his first part because he sets the tool length to the physical end of the spot drill and not the V-point.
By comping to the virtual point Roger can in effect cut to the pitch diameter which is what the wires are measuring. It is harder to do without a magnified optical presetter and for threads it takes some practice. At 03:00 PM 6/29/2007, you wrote: >Roger: > >The actual depth of the thread is not really important. It is the angled >surfaces width that is. That is why measuring with 3 wires is the most >accurate. The wires only touch the angled sides of the thread. Actually >there is a formula for figuring out the best size of the wires as well. >But if just comparing threads, just use an appropriate size wire-meaning >you want the contact point close to the middle of the angled depth. >In the machine shop I worked at we would measure the spindle nose thread >with 3 wires - machine a thread gauge (same as the spindle) confirming >it's size with the 3 wire method then would use that to test fit the >internal thread. we would stamp the gauge and keep it safe for next time! > >Of course if you have something handi that fits the spindle you could use >that to test fit while making the thread gauge-then you would not need to >measure at all-if you are careful. It all really depends on how good a fit >you need and how much time you want to spend and what you have for tools! > >Cheers >Chris Morley > > > > > >---------- > > > From: [EMAIL PROTECTED] > > To: [email protected] > > Date: Fri, 29 Jun 2007 11:23:36 -0500 > > Subject: [Emc-users] Lathe Threading > > > > First of all, thank you developers for EMC and thank you John Kasunich > > for getting the m5i20 threading working. I loaded the pre 2.1.7 version > > and built it on my pc, the threading worked first try, I only had to > > change my old latch-index to index-enable and then tested it out, I now > > have a lathe pawn with threads! > > > > In wondering about setting up to cut threads, I thought perhaps I could > > set my threading tool as if it came to a shap 0 radius point and thread > > the full depth from that imaginary point. I drew a 60 degree point in > > AutoCad, drew a line through the point, then applied different radius' > > to the point. For a .008" radius cutting tool, there was .008" between > > the tool tip and the line representing point, for a .0156" radius, there > > was .0156" between the tool tip and "point", and so on. The tool tip > > radius equaled the gap between the peak of the radius and the 0 radius > > point. > > > > So, I was wondering if I used a threading tool with a .008" radius, > > could I take a light test cut, measure the radius, add .008" set that as > > the X position of that tool, then thread to the full thread depth. This > > would put the imaginary 0" radius point at the full thread depth and > > actual point .008" out from the full thread depth. This procedure could > > be adapted for whatever tool tip radius you were using. If a test cut > > wasn't practical, you could use feeler gages to set the tool, as long as > > you knew the tool tip radius. Or perhaps there is an easier way I'm > > overlooking :-) > > > > I plan to try this out, perhaps I could learn how to measure with the 3 > > wire method and see how close the threads came out. My goal is to come > > up with a method that will give me the right thread depth with minimal > > trial and error. I have a project of machining a back plate for an L&W > > dividing head, the thread is 2-1/4 10tpi. I dread test fitting the > > dividing head to the back plate! > > > > Roger Neal > > __________ Andre' B. Clear Lake, Wi. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
