Having a bad day?
There's nothing wrong with grinding down a plug tap. When I've got some parts to turn quick and I don't have the proper tap it's no big deal to grab a plug tap and grind it flat to make that part. I don't see how it gives a better thread, could you expand on that? If I'm wrong here or have something to learn I'd love to not do more dumb shit. That said, if you don't fuck the tap when grinding it down, there's nothing that's going to cause issues. I use TSC and take it a little easier and haven't had a single issue with fucked up threads (plus I didn't have to wait on a tap)...
M4 is not a designation for depth (at least I've never seen anyone callout M4 over 4mm when designating length or depth), the drawing also doesn't say anything about 4mm thread depth. I'm fairly certain whoever created the drawing made a mistake and for whatever reason threw in M4 where they should've called out an actual depth. Or maybe I'm wrong, which definitely isn't unlikely.
Yes, which is why I said contact them. However that's not always possible on an off shift with tight deadlines. We farm out a lot of parts and mistakes happen when our engineers miss something on a drawing. If they can't contact us it falls on us and if they guessed wrong I'll have to rework the parts in house. If you get a drawing that's incorrectly drawn up and you make it to that, are you responsible or is the person who sent it over? I know there's a lot of stories on here of it going both ways. But, you're right, maybe calling it on them and tapping to full depth isn't the best move... but how long are you going to sit on a job and tie up time for someone else's mistake? It's not clear cut. Tapping to full depth (or as close as possible) is more than likely what they're looking for. I've also seen engineers kick out drawings without a depth called out assuming you'll tap to the called out drill depth, for whatever reason.
The attitude its "on them" really sucks and its a piss poor attitude to have. you just dont run it with out being 100% sure and wait for an answer. its one thing if your know your customer and knows what they want, or its your own parts. but not knowing and using a answer on the net can be hazardous, as the people taking the guess's have no skin in the game.
typically if theres a min. call out then its open as long as you make that MIN FULL thread.
if theres only a depth for the tap lets say .200 deep then its full thread .200 deep plus or minus your tolorance what ever it is.
Blind holes generally have a call out for a few reasons most blind holes are short and they want xxx amount of minimum thread, sometimes they require you got to bottom of the minor dia. flat and that doesnt mean a modified tap going to the bottom, they will usually give a optional sheet that shows a counter bore a hair over the major size in which you have to use a key cutter to do it( we do a ton of these) then tap it. Then there some that want it "close" to the bottom well what exactly Close different meanings to different folks. close could be a standard bottoming tap, a modified 1.5 bottoming tap or even a hand ground less than 1.5 modified bottoming tap.
This one appears to have alot of thread for a blind hole. other reasons I have seen is they want to screw down something to a certain depth like a stop or bumper. or there putting a helicoil in it and dont want the guy putting in the helicoil to go to deep.
I dont do alot of metrics anymore, never seen a call out like that. unless they stated M4 meaning thread dia? then made a Rev change later clarifying it in RED thats its a M4x.7 theres a whole bunch of senerios the way it could be called out, with out knowing the customer, or seeing the whole print we will never know.
I had one customer about years ago, that they refused to call the customer if I had a Print question.I dont understand why maybe laziness or felt they were looking like a fool for asking, embarrassment.... I have never figured that out. they had the Same attitude as you have (its on them if its wrong). one day I got tired of the shit and reworking parts yeah they were paying me for it. so I called their customer direct of coarse telling My customer I wasnt going to run the parts unless I got confirmation and I want to talk to them.
of coarse my customer was wrong in his assumption of what it read. about a month later he and his customer and 4 of there engineers showed up at my shop going over all there print discrepancy that I told them about. it helped my customer alot cause they got so much machine work they actually had to fire there machines up to do my overload. not to mention they had no Discrepant parts
There engineers were from a major US medical company the engineers were foreign all but one was fresh out of school, they didnt understand simple things, not to mention they used solid works and snapped everything and rounded off 2 place decimal
Its never a bad thing to call your Customer to verify, scrap parts no matter whos fault sucks and doesn't give a good impression. Not to mention it shows your observant and competent.
BTW a mediocre and low budget plug taps ground on a m4x.7 going deep like that in a blind hole generally doesnt give a nice thread, chips are bad on most plug taps depending on the material, alum sucks with m4x.7 plug taps going more than .200 the m5 isnt much better the m6x1 6 isnt a problem