Jim hello again let me stress the word 'scale' most google hits will claim edm has 'no burr' thats a damn-lie (tm) invented by sales-people i can feel it with my finger tip IF it was done fast on a cheap machine so there is a sliding scale of burr height from nanometers to tens of microns
the burr height is related to current at entry/exit (not solely dependant, bit its a biggie in the picture) so you can get less burr if you reduce the power at entry and exit http://bit.ly/2l6hvkx the url shows edm hole burrs, it uses SEM photos ( scale again :-) my discussion before was cheap taiwanes hopops if you use an sophisticated(read expensive) machine ( say sarix or sodick or hitachi ) you will get control over the entry and exit power and hopefully control over the control method at exit changing from gap control to feed control at exit helps because when you exit the hole, there aint no gap, theres nothing in front of the tool tip at that time the gap width control fails and the control begins to bang into that last tiny bit of stock hanging on the edge of the cave exit and you get some nasty micro short circuits and some scraggy exit edges if the control system is bad enuf, you actually push the remaining stock out! again, its magnitude/scale, so take a sample part to a jockey (aka applications engineer) and see what result you get thats a good feasibility/reality test On 02/12/17 01:27, Jim Craig wrote: > On 2/10/2017 9:01 PM, TJoseph Powderly wrote: >>> The reason I am contemplating the small hole EDM process is three fold. >>> First it is difficult to drill these tiny holes in stainless and the >>> drill bits frequently break. Secondly the back side of the hole needs to >>> be burr free but is difficult to get to with conventional tools. >> scale again... 'burr free' >> well edm produces a burr, its small a few thou to 10 thou depending on >> energy at breakthru and the system ability to control position well >> ( hammering thru with bang bang control has larger burr ) >> to get almost no burr, use a sacrificial plate and burn thru the SS and >> into the sacrifice > I will have to reconsider if it does not make a burr free hole without a > backer. I was under the impression it did. I guess what I was reading > was with a backer or a stack of parts. I am not sure if the client would > consider a 10thou burr acceptable. 10thou is large and the size can be controlled at the expense of time ( small burr needs small current. small current = larger time ) Afaik there will always be some burr, but i'm talking tiny. > This is a spherical part where we are drilling through the spherical > shell into the hollow center. Some holes are off center again benefiting > from the EDM process. yes drilling off center on a ball is something the hole drill edm can do it requires a bit of control work , its like riding a horse down hill on gravel a lot of this is the driver/jockey controlling the machine, picking the right adjustments and having a good machine. > We could possibly have fluid (water) in the core of the sphere would > that help reduce the burr? yes it will help, drilling from wet to dry will aggravate it so 'help' is what it will do, it will not 'fix' the exit problem > Snip >> sorry i gets carried away with edm stuff >> tomp tjtr33 > No reason to apologize. You have provided lots of good information here. > > Thanks a bunch, > > Jim > thank you tomp tjtr33 > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, SlashDot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, SlashDot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
