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tapping vs machine thread screws - where does everyone stand?

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Hi TamiyaClub,

A bit of overthinking :) Just curious to see what opinions everyone has on 3mm tapping screws vs. M3 machine scews whenever screwing into plastic.

It seems like the "modern" way is to go with machine threads more and more. Tamiya often sells a(n overpriced) Titanium screw set that is all machine threads. People probably buy it more for the hex heads than the weight saving. Also if one looks at the TT-02 timeline the original one was all tapping screws but the Type SR has machine threads now. Then the M06 from 10+ years ago has an interesting mix and match of both types of screws!

I always do the "turn counter clockwise until it clicks" method before installing any screw in an existing threaded hole to avoid destroying the plastic and haven't had any issues with tapping screws. Now I wonder if I would be able to do the same with machine threads.

Thoughts?

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For me, I hate Philips/JS screw heads. I like the look of Hex heads button or counter sunk. If I could easily get Hex self tapers I would use them BUT machine screws of loads of sizes is way easier. I have been taping the holes first for M3 and never had any issues. I have even used machine screws in old holes and they have held. I think you can strip machine more easily,so take care. I have read lots a bout the different types of plastic used and strength areas BUT as a wise man as said " its a toy and I am not sitting in it" So if I have a suitable size the tappers come out.

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I’m fine with either screw, depends on the material.   Vintage RC plastic (like my M38’s front arms) is pretty fragile so I would use machine screws into plastic at lower torque until the day it might strip, and use tapping screws after that, then use CA at the very end.   Then replace the entire piece if it is completely stripped where I can’t fit a larger diameter or longer screw in there.   
 

I get picky using countersunk hex head screws on dual deck CF chassis however.  Those are precision chassis and like everything flush and clean.    Vintage RC, non-CF deck chassis, not so much.  

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I always use hex head machine screws... but you should never 'tap' the holes in plastic. Tapping removes material, leaving the screw more prone to pull out or strip when tightening.

Use a thread former rather than a fluted tap: Tamiya do an overly expensive one, but you can pick up both right and left (good for ball cups for the other end of turnbuckles) handed "Thread Forming Taps for Aluminum" from China on eBay.

RH Thread: https://www.ebay.co.uk/itm/402439674258?hash=item5db3461992:g:wu0AAOSwIftfYjMI

LH Thread: https://www.ebay.co.uk/itm/402403518030?hash=item5db11e664e:g:VcwAAOSwHfdfTys2

The size you require is 'M3 x 0.5'

Martin.

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In most places where Tamiya specifies a tapping screw, I install the tapping screw Tamiya specifies using the "hot screw method" for fresh plastics. This involves heating the screw before installing into a fresh hole to help remove/reduce the pressure caused by normal screw installation. In ABS/PC plastics this cuts down on the micro fractures (caused by initial screw insertion) that become cracks years down the road and eventual component failure. There are exceptions like the rear shock mount that goes into the trailing arm of an ORV type vehicle. In this specific case I do use a machine thread screw (in conjunction with the proper thread forming tap) capped by a nut on the backside.

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That is a lot of interesting info from everyone! Martin I had never even heard of a thread former.

I also wanted to mention that I use machine thread a screw is the kingpin; the finer pitch (compared to tapping) allows for a nice "micro adjustment" of the friction, for that perfect no free play & no friction setup.

I was also tempted to use grease when forming a hole in hard plastic for the first time with machine screws. Sometimes the screw becomes extremely hot as you thread it in and the plastic starts making a squeaky sound. I guess that is the hot screw method unintentionally.

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For me the choice depends on the kit and application. Most of the kits I've done recently have used the more modern tamiya composites rather than the black shiny stuff so I've used hex head machine screws, but if I was restoring vintage or building something like a grasshopper I stick to jis self tapers for most of it. 

The head choice matters less to me than the thread type - I prefer hex head, and typically you won't find hex head self tappers, but some applications require a self tapper. 

I think any current / future mid range and up kits from tamiya will be fine / compatible with machine screws (e.g m07/m08/cc02/ta07/ta08/xv01 have very few if any self tapping screws) - ball headed hex drivers also make installation easy at tricky angles!

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Yeah... depends on the kit for me too.

Whilst I prefer machine screws, I stick to what the kits are supplied with just because I like my kits built 'stock'.

If I was running a kit seriously though, then I would swtich them all.

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Prefer JIS self tappers, if tamiya deems using a hex head and i havent got a JIS to hop it up then I stick to what is supplied

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The comparison is invalid...

Machine threads aren't self-tapping... so they're not a direct replacement for self tapping screws, period. You'd never interchange them. You can get thread forming machine screws but that's not what Tamiya sells and they're referred to "thread forming" rather than "machine" (to avoid the ambiguity). Machine thread screws are made to mate with a tapped or threaded nut or hole.

What's actually important here is that Tamiya make utterly rubbish screws, regardless of whether they're JIS, socket, self tapping, machine, titanium or anything else. For 1/3 of the price of a Tamiya screw kit you can get a far, far superior product from somebody that knows how to make (or procure) proper screws. The titanium screws that Tamiya supplied in the early 90's were 1000% better quality than the (Ti) ones they provided for their TRF kits in the mid to late 00's. They cheaped out on their customers.

The JIS v Philips v socket head screws is a different discussion.

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Every one of my Tamiya builds gets Allen head machine screws throughout. It makes maintenance enjoyable, and my cars don't ever have random bits falling off or coming loose every run.

The only reason in my book to use self tapping screws is if you want a box stock build for a shelfer. Tamiya should use quality hardware on everything other than base entry level kits, including all rerelease kits.

 

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As a tangent...

I recently bought a Fire Dragon screw kit from Ebay.  It sucked.  Missing screws, etc.  So I decided to do the work and piece together my own.

I was able to find stainless steel M3 machine and M3 tap screws, with hex button heads.  I was also able to get M2.6 tap screws (with Phillips heads - maybe JIS???).

eBay seller:  "superiorsell2014"  https://www.ebay.com/usr/superiorsell2014?_trksid=p2047675.l2559

I haven't used them yet, but they look nice...

Terry

 

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Most of my runners have 50+ hours of run time with no issue with JIS, anything else is unnecessary.

Tamiya normally leave a good handful of screws as leftovers so after a dozen builds or so you have spares for life if you need to change any rusty ones over etc....

The only model where parts have loosened has been the rere terra scorcher due to the small vibration of the gear molding, once it bed in, problem gone

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I don’t think this was a technical question, more on what individuals prefer.

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I’ll tell you what…. Once I got rid of my Phillips driver and got a JIS driver, it made a huge difference on the stock screws…

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Everything that tamiya does regarding what they include with kits is ok with me

self tappers, JIS screws, plastic bearings etc........its the prices that could do with being reduced slightly and availability of spares/hop-ups!

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I really wanted to know what people prefer and why. Myself I just enjoy wrenching more with hex hardware. I can feel how much torque I'm applying better if I'm not busy pushing on the screw to prevent the screwdriver from popping out. And I have a genuine Tamiya screwdriver :D

I think at that point even if I'd do a re re Grasshopper I'd go out of my way to convert every possible screw to hex head. It's just what I prefer.

2 days ago I struggled with a Phillips screw on the motor pod of the used f104 ver.II that I'm restoring, previous owner used way too much loctite and that was probably 10 years ago at least. The Phillips head quickly stripped. I had to make a special fixture for my vise and eventually won the battle, but what a pain.

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