I agree, tapping that depth in aluminum is just asking to gall the threads. If you have a decent alloy (6061 7075) you only need 1/8” to hold what ever is save to hold with a #4. If you need more strength then it would be best to use helicoil inserts.
Where are you located? There are a number of hacker spaces across the country / globe. If you are in the US, there is also "The Tech Shop”. If you are in the SF Bay Area I would take a look. Link > On May 18, 2017, at 11:16 AM, Tim Shoppa <[email protected]> wrote: > > I'm very dubious that you need a tapped 4-40 hole to be threaded any deeper > than 0.25". If you work with the machinist I'm sure you can come up with > some reasonable spec that does not require a bottoming tap and will save > you a lot of money. > > I bet you went to 0.25" wall square tubing only because you want to tap the > walls for 4-40. Alternative designs can let you use much thinner material > and a very different flange on the ends, but the costs will likely move > towards welding/brazing rather than machining. > > Tim N3QE > > On Thu, May 18, 2017 at 12:54 PM, <[email protected]> wrote: > >> Hi, >> >> I have a square aluminum tube 5" X 5" with a .25" wall it's 8 1/2" long. >> >> I need 20 holes in each end tapped for 4/40 and 1/2" deep. >> >> This is for a Rubidium project. >> >> The local machine shop want's $360.00!!!! >> >> Anyone have a machining setup that could do the work a bit cheaper? >> >> If not I'll give it a try myself. >> >> Please contact me off list. >> >> Thanks! >> >> Corby Dawson >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/ >> mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
