Hi,
I noticed there are a couple of M5 locating holes on the N3 table.
Can anyone coment on their purpose, moreover their suitability to
house precision pins to locate a custom modvise? I’m particularly
interested in whether their location in the Y direction could locate
an edge in the X direction parallel to the X carriage.
To be fair, I shall probably machine the modvise base once located
anyway so the locating edge matches the X carriage.
Relatedly, I purchased some M5 dowel pins but find them to be 5.01mm
according to my very cheap micrometer and they not going to fit the
holes in the table without some serious violence I’m
new to all this fitting tolerance lark, anyone advise what I need to buy
to make a “location fit” with the table?
I usually used the 6mm locating holes for alignment as that’s what Carbide 3D used for their vise and flip jig.
And regarding the use with a mod vise, you might want to consider using a threaded table and putting partially threaded pins like these in it instead. That’s what Saunders Machine Works does with the metric bed + mod vise (the imperial one has fancier pins). This gives you many more places on the table to mount the vise, so the vise doesn’t have to travel so far, so it can be more compact.
Nitpick: M5 is a designation for threads, there’s no such thing as an “M5” locating hole or an “M5” dowel pin.
As for the diameter, you need to be careful about the tolerance of the dowel pins you buy. There are dowel pins meant for slip fits and locating (usually tolerance h6) and there are pins meant for transition or interference fits (e.g. tolerance m6).
You probably bought the latter category of pin, which could have a tolerance like +3/+11um.
The main thing to look for is the letter. The “h” set of tolerances never exceeds the specified diameter. It’s always -something/+0.
Regarding all the fits and tolerances stuff, I can’t recommend enough buying a reference book about it. In the US the standard is Machinery’s Handbook and for the rest of the world there are other books. Personally, I use this one.
I’d also recommend a textbook. I went for this one.
Yes, sorry, I had been tapping M6 and M10 continuously on my most recent project and my brain was wired for threading, of course I meant 5mm.
Thanks for the hints on fit designations, I’d found some tables online but you made the point far more clearly… really helpful!
I’ll order some h6 pins and see if they fit. Worst case I’ll have to see if I can make some brass ones in the lathe.
I don’t know what the tolerances on the holes is but I can say for sure that 6mm h6 pins fit quite comfortably in the 6mm holes, so I’m fairly certain 5mm h6 pins should fit in the 5mm holes.
@Moded1952 thanks for the book recommendations — especially the “Mechanical and Metal Trades Handbook” (Mechanical and Metal Trades Handbook - Europa-Lehrmittel). I like how things are presented there, and it (mostly) describes the metric world, really valuable for people in Europe!
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