Rant Time - TIP35 Transistor Hole Size (Resolved) - Page 1
Forum section: electronics / general

author: German_EE
author_rank: Super Contributor
timestamp: September 10, 2015, 08:54:54 pm
content: Somebody please find the person responsible for specifying the hole size on the TIP35 transistor then take him out back and shoot him, more than once. The hole is specified as 3,55 to 3,65 mm diameter (so let's assume 3,6mm) but:This is too large for a 3mm bolt and too small for a 4mm bolt.Nobody local has 3,5mm bolts and 3,5mm taps are as rare as rocking horse droppingsThe nearest Imperial size to 3,6mm is 9/64 or 3,57mm, another weird size.Life would be a lot easier if people created devices that had standard hole sizes such as 4mm and 1/8 inch but clever folk like the designer of this transistor just have to be different! Still, I have a solution, tomorrow I'm going to drill out fifteen transistors to 4mm then use a standard size bolt to fix them in place. I wonder if I can bill ST for my time?

author: Andy Watson
author_rank: Super Contributor
timestamp: September 10, 2015, 09:02:44 pm
content: Try a 4 B.A.

author: donmr
author_rank: Regular Contributor
timestamp: September 10, 2015, 09:04:27 pm
content: That's a good size for an ANSI 6-32 screw (0.1372in, ~3.485mm) but most of the time I use an insulating insert and smaller screw.

author: ajb
author_rank: Super Contributor
timestamp: September 10, 2015, 09:09:56 pm
content: Yep, there's a whole set* ofperfectly standard fastener sizesthat have zero discernibly logical relationship with standard units of linear measurement.*actually several sets, but Metric and UTS will cover most applications, and at least metric mostly lines up with reasonable drill dimensions. For UTS drill sizes, you want numbered gauge drills.

author: langwadt
author_rank: Super Contributor
timestamp: September 10, 2015, 09:29:35 pm
content: Quote from: German_EE on September 10, 2015, 08:54:54 pmwhy do you think it is too big for a 3 mm bolt? there's has probably been fitted millions of transistors with m3

author: TimFox
author_rank: Super Contributor
timestamp: September 10, 2015, 09:33:04 pm
content: The unified series of American thread diameters is approximately exponential or geometric, not linear. There is aroughlyconstant ratio between adjacent sizes. This is similar to American wire gauges and standard resistor values. Some odd sizes (7,9,11) are not included. A useful set of sizes is 6-32 UNC, 8-32 UNC, and 10-32 UNF. As you wear out the female threads (starting with 6-32), you have two opportunities to re-tap to a larger diameter.

author: wraper
author_rank: Unknown
timestamp: September 10, 2015, 09:33:09 pm
content: Quote from: German_EE on September 10, 2015, 08:54:54 pmLife would be easier if not ranting about nothing. Did you hear about such a thing like insulating bush? BTW this have nothing to do with particularly TIP35, this is standard TO-220 case. Also 3.6 mm is nowhere near being too big for M3 screw.QuoteM4 screw often will not fit into 4mm hole or will be hard to insert.QuoteWhy should they pay for stupid and useless effort?

author: John Coloccia
author_rank: Super Contributor
timestamp: September 10, 2015, 09:35:55 pm
content: 3.6mm is the proper "loose" fit clearance hole for an M3 bolt.I don't mean this as any sort of sarcasm or anything like that, but go out on the web and download:-combined metric/imperial equivalents and drill sizes chart, including number and letter drills.-metric and imperial tap drill chart-metric and imperial clearance hole chart, listed with tight/normal/loose clearancesPrint them out and pin them to the wall. I probably have about 5 or six complete collections kicking around. Some are stuck to various tools with magnets so I always have access to them at a glance in the wood shop. You'll thank me some day.

author: lowimpedance
author_rank: Super Contributor
timestamp: September 10, 2015, 11:15:36 pm
content: Quote from: John Coloccia on September 10, 2015, 09:35:55 pmAbsolutely essential for every workshop, wood/metal whatever, if you need to drill and tap anything !.

author: langwadt
author_rank: Super Contributor
timestamp: September 11, 2015, 12:16:29 am
content: Quote from: lowimpedance on September 10, 2015, 11:15:36 pmas long as you stick to metric, tap holes are easy, for most materials it is just the diameter minus the pitch

author: lowimpedance
author_rank: Super Contributor
timestamp: September 11, 2015, 03:10:49 am
content: Quote from: langwadt on September 11, 2015, 12:16:29 amEasier said than done , but for a hobbyist workshop yes you should try to stay metric however the charts are still great to have 'when needed'.

author: TimFox
author_rank: Super Contributor
timestamp: September 11, 2015, 07:30:09 pm
content: Quote from: John Coloccia on September 10, 2015, 09:35:55 pmI totally agree about these charts. I have a hardcopy poster from a tool vendor prominently placed in my garage work area, that has all sensible American drill sizes (number, fractional inch, and letter), sensible mm values, etc. arranged in ascending order. Each entry has the decimal inch and mm size posted. This allows me to pick easily a standard drill size to fit a measured object, whether the nominal size is inch or metric.My favorite metric screw size is the standard tripod-mount thread for small cameras, which my camera manual identifies as M6.3. It sure looks like 1/4-20 UNC to me.

author: SeanB
author_rank: Super Contributor
timestamp: September 12, 2015, 07:43:19 am
content: 3.6mm is a standard rivet size, and a lot of the TO devices have a fixing method which is permanent using a pop rivet to provide the clamping force required. M3 with a insulating bush fits the hole perfectly. Otherwise a M3 tap and a countersinkk drill to deburr the hole in the heatsink are easy to do, though if you use old PC screws they are slightly trilobular, and will cut the thread into the hole by themselves so obviating the need of a tap in this case. They are designed to do so into the punched sheet metal of the case.

author: poorchava
author_rank: Super Contributor
timestamp: September 12, 2015, 09:29:51 am
content: Also standard washers for M3 screws are 5.5-6mm OD, so it should work ok.

author: G7PSK
author_rank: Super Contributor
timestamp: September 12, 2015, 03:42:04 pm
content: No one but no one should be without a Zeus chart.http://www.amazon.co.uk/Precision-Reference-Drawing-Toolroom-Workshop/dp/B0000CLZUO

author: TimFox
author_rank: Super Contributor
timestamp: September 12, 2015, 04:59:12 pm
content: I just looked for the wall chart (from SPI) that I bought a few years ago, and it seems to have been discontinued. Probably because of all the free PDF versions available (but not in large format with plastic lamination). Luckily, I bought two.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: September 12, 2015, 08:49:18 pm
content: You can take your free .pdf chart of choice to a local print shop and get it converted to a large laminated version. The cost will not be horribly higher and possibly a little lower) than the purchase price of these when they were easily available commercially.The real advantage is that with a little FOSS software you can customize those charts to your own needs. (Your wall space is wide but not very tall, no problem. You need Whitworth sizes. No problem.)

author: German_EE
author_rank: Super Contributor
timestamp: September 13, 2015, 03:43:21 pm
content: The issue is now academic as a spent ten minutes drilling out the transistors to fit a 4mm bolt and then forty minutes drilling and tapping some suitable holes. My next issue is testing a DC Dummy Load that can (in theory) handle 250A @ 70V. The 6mm copper bolts used as connectors on the front panel should handle the current but I may need to find some welding cable.Yes, the heatsink is very big

author: wraper
author_rank: Unknown
timestamp: September 13, 2015, 03:55:22 pm
content: If this device passes to someone and transistors fail for some reason and needs replacement, I already can imagine:Quote

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2015, 04:11:05 pm
content: Quote from: wraper on September 13, 2015, 03:55:22 pmCould be worse, he could have gotten some copper busbar, milled the top and bottom faces flat and then soldered the devices to it with solder paste, then mounted the whole lot to the heatsink with high tensile rivets and thermal compound.

author: Augustus
author_rank: Regular Contributor
timestamp: September 13, 2015, 05:45:57 pm
content: Quote from: German_EE on September 13, 2015, 03:43:21 pmThat thing should come in handy in the upcoming cold winter months

author: SeanB
author_rank: Super Contributor
timestamp: September 13, 2015, 05:55:15 pm
content: M6 and 250A is not going to end well. At a minimum you need M10 brass bolts, which will only get warm. The mains busbar in the substation at work is rated for 400A, and uses M12 hardware for the main power connections. The tails for the sub boards off the copper bus bars are only rated for 100A, and use M8 hardware. Cable is 16mm for most, though the breakers are 80A, the lift uses 25mm cable and has a 100A breaker.