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Anyone know of any 3mm tapping countersunk hex screws that can replace tamiya JIS?

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A bit of a random one but I recently brought a load hex head tapping screws to retrofit to various models just to make them a bit easier to work on and more uniform without the need to try and convert to machine thread. 

The only thing I'm having trouble with is the countersunk screws. M3 machine thread/hex head screws have a head diameter around 5.7-6mm but TAPPING countersunk/hex head all seem to be 6.8-7mm so they wont fit into the chasiss holes properly.

Anyone ever seen anything suitable? I know most people either stick with the stock JIS or convert to machine thread but I'm been working on a lot of older cars that already have threads in them from self tappers so these hex+tapping screws have been a great compromise.

Failing that, what's the best way to go to machine screws? Can you just screw them straight in or is it better to use a tap to make a thread? Are the holes large enough to tap fresh out of a kit or do they need widening? And if the holes have already had self tappers in will they be too loose to use machine screws?

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Tap the threads, it's very therapeutic, and satisfying once finished and everything bolts together so nicely. 

Gonna do it to all my builds from now on.

You'll struggle tapping pre screwed holes, but fresh holes just need a 3mm 0.5 tap.

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I love tapping threads. I tapped every single screw hole on the M07 and all the holes on the TT02 hard blue chassis before assembly. Screws fit in so much more easily and lock in with a satisfying change in torque that is easy to detect, which helps avoid stripping.

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I'll be honest I have had bad experiences with thread forming taps and plastic including the plastic cracking and splitting. I seem to get the plastic springing back to shape afterwards too and resulting in the screws being super tight.

Always found a fluted tap works better by removing some material even if the overall strength of the threads is technically weaker. It just seems to put less stresses on the plastic. Ymmv.

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The thread tap I use is fluted, and I've had zero issues so far, but to be fair I only use it on strengthened plastics and not the soft type. It does create some shavings when I use it, but it's a really small amount.

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The Tamiya tap in the UK is like £20, I saw the price and just thought forget it. The fact that you can get a set M3 1st, 2nd and 3rd taps by the likes of Presto or Dormer for much less sealed the deal for me.

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I've been using these on both soft and reinforced plastics, instead of the Tamiya thread forming tap (which I also own), for the last 15 months with no problems... put a fresh dab of Vaseline on the tip (I keep a lip salve tin on my workbench for this) before cutting a thread and clean with a brass wire brush when they start to clog. The advantage is I can easily do ball connectors for turnbuckles with the left-hand thread.

 https://www.ebay.co.uk/itm/Select-Variations-M1-2-to-M22-HSS-Right-Hand-Thread-Forming-Tap-for-Aluminum-/113917056796?var=&hash=item1a85fc571c

https://www.ebay.co.uk/itm/Select-Variations-M2-to-M16-HSS-Left-Hand-Thread-Forming-Tap-for-Aluminum-/123932650618?var=&hash=item1cdaf62c7a

You'll want them in M3 x 0.5 size.

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