Anyone lately go full machine screws and ditch Tamiya self tapping?

[Doglover]

I use mostly M2, M3 and M4 allen headed cap screws (Machine Screw) to replace Phillips or JIS self tappers. But then I cut a shallow vertical slot in the last three threads of the cap screw with a Dremel cut-off blade to create a slight tap effect - then use a bit of hand soap for lubrication.

Goes in great, doesn't damage the plastic and looks way better.

[TwistedxSlayer]

Kit build are done with the tamiya screws.

 

All my rebuilds and projects are done with machine screws, dome hex, Allen key cap or countersunk hex heads.

[Big Jon]

To be blunt, wood screws are for wood. Machine screws are for machines. There's no benefit to using self-tapping screws on our kits other than ease of initial assembly for rookies. They're less reliable, strip their holes easier, loosen with use, and wear out their holes with repeated disassembly/assembly.

I've used hex head machine screws on everything from Grasshoppers to MF01. All of my restorations get hex hardware. All of my new builds get hex hardware. When I repair customer's cars, any brand, I use hex hardware. A lot of Traxxas cars use butter soft Phillips hardware, both machine and self-tapping, and it's always bent if it's in a high stress area. Quality hardware fixes a lot of reliability and durability issues before they happen.

Yes, everyone owns a Phillips or JIS screwdriver, and you need to use quality hex drivers with hex screws. I understand the rationale behind using commonly available screw heads and self tapping screws on entry level kits. Entry level builders aren't going to have nice tools, won't tap threads, or grease screws. That's fine. Quality hardware is a massive upgrade on any kit that will be used.

[Fabia130vRS]

The only time I use machine threaded screws is if added aluminium upgrades, fluorine ball connectors, carbon upgrades and other. I dont put them on plastic parts of the chassis unless the I dont really have another in matching color.

[rich_f]

7 hours ago, Big Jon said:

To be blunt, wood screws are for wood. Machine screws are for machines. There's no benefit to using self-tapping screws on our kits other than ease of initial assembly for rookies.

I wouldn't call them wood screws - wood screws are pointy. I'd call them 'screws for soft material', like plastic. 

How many times have you taken some plastic machine/appliance apart and found machine screws driven into plastic parts? I can't recall many, if any. They are invariably coarse-threaded tapping screws when the screw goes into a plastic part.  

Machine screws are for hard materials, usually metal. Even then, softer metals use coarser threaded machine screws - when I was rebuilding my mini's a-series engine, I noted that all screws into the cast iron block or steel parts were unf (fine), while those threaded into the aluminium transmission housing were unc (coarse). 

You might say it's for convenience that tapping screws are used in plastic, but they could just as easily use fine-threaded self-tapping machine screws (i.e., with a slot cut in the thread). I think the real reason is that the coarse-threaded tapping screws simply have more 'bite', as has been mentioned before. The threads are physically larger (and the shaft correspondingly thinner) and dig into the plastic thereby affording greater pullout strength vs shallower threaded machine screws.

Google 'screws for plastics' and you'll get a lot of results that look just like tamiya tapping screws, and lots of information on why that type of thread form is used. What you won't see is machine screws. 

Needless to say I've never replaced any tapping screws that are threaded solely into plastic with machine screws, except for when I put frp shock towers on my ta02 - it came with machine-threaded step screws which replaced the tapping step screws for the plastic upper arms. My only guess is that tamiya expected me to replace the upper arms with adjusters with ball ends, meaning a ball nut would go on the machine step screw. I eventually did, but for the in-between time that I didn't, it felt wrong having that machine screw going into that soft plastic.

[Saito2]

1 minute ago, rich_f said:

I think the real reason is that the coarse-threaded tapping screws simply have more 'bite', as has been mentioned before. The threads are physically larger (and the shaft correspondingly thinner) and dig into the plastic thereby affording greater pullout strength vs shallower threaded machine screws

I agree. This is the other reason I stick with what Tamiya uses. Again, the holes Tamiya molds are quite likely designed with this in mind. The "shaft" is referred to as the fasteners minor diameter. There is a measurable difference in the minor diameter of a Tamiya self tapper vs a Tamiya machine screw. I would imagine to be completely "proper" in making the switch to machine screws from self tappers, the hole should be drilled out to the appropriate size (which may not honestly be required or easily done as many Tamiya molded holes tend to be triangular when intended to receive self tappers) and a thread forming tap used.

[Alexei]

i prefer hex machine screws, i found it easier to work with. i have assembled my TT-01, TT-02S and FF-03 with hex screws. before installing any screws, i threaded the holes with Tamiya M3 threading tap (54232).

[El Gecko]

15 hours ago, rich_f said:

I wouldn't call them wood screws - wood screws are pointy. I'd call them 'screws for soft material', like plastic.

Exactly! I would also submit that Tamiya got their self-tappers perfectly correct for the application. Other vintage screws (Traxxas) have much larger thread pitch, even though they're the same size screws, which makes them more prone to backing out and stripping out. I've been replacing that type of hardware on my Traxxas trucks with Tamiya self-tappers and they seem to be holding up a bit better. I can drive them for longer before I have to retighten everything.

[nowinaminute]

On 1/30/2021 at 7:43 PM, nowinaminute said:

You have two choices with taps as far as I know. The kind that removes material and the kind that displaces it. The former type supposedly defeats the object a bit because it results in smaller threads and the latter type doesn't really give a functional advantage over just using a screw.

Well as chance would have it, I decided to have a go with one of the "inferior" thread "cutting" taps today. Supposedly the cutting type are inferior to the "forming type" 



But it got me thinking that maybe with plastic, the latter type would be safer as it puts less pressure on the material.

So what I did as an experiment was drill out a Tamiya hole intended for 3mm tapping screws using a 2.5mm bit to make it ready for the tap. It barely took any material away to be honest. Then I used an m3 "hand tap" of the fluted cutting type to cut the thread into the hole. I used the "2nd cut" type which is half way between the highly tapered "1st cut" and totally straight "3rd cut"

This resulted in a nice clean thread and when I put a screw in it went in nice and smoothly, nice and secure but not the creaking, popping tightness you get just putting a screw straight into the plastic. The screw when in smoothly all the way and gave very clear and positive feedback that it was fully screwed in. You'd have to be a bit daft to strip it, put it that way.

I have to say I'm pretty pleased with the results. Like I say, a "forming" tap that displaces the plastic might put a bit too much strain on the plastic but then again, that's the type Tamiya sells so maybe it would be ok if you drilled the hole to 2.5mm first? Might give it a try.

I think I might take that approach from now on. Not perfect perhaps but it seems to result in a nice strong thread and it's certainly not putting as much outward strain on the plastic as putting the screw straight in does, even with grease.

What I was perhaps more pleasantly surprised with was that it seemed to work great for tapping holes that have previously been occupied by a tapping screw. When I have just tried putting machine screws straight in to such holes it has never worked well for me but using the tapping tool first and then putting the screw in gave a nice positive feeling and a firm feedback of when the screw was fully tightened home. It felt just like the blank hole I taped to be honest!

Pleasantly surprised overall. The tap was only 99p from UK Drills on ebay too!

[NulnOilTycoon]

I guess another question would be why on Earth can't you get m3 stainless steel, titanium, etc. tapping screws with hex fittings?  Surely someone makes them?

[Juhunio]

18 minutes ago, NulnOilTycoon said:

I guess another question would be why on Earth can't you get m3 stainless steel, titanium, etc. tapping screws with hex fittings?  Surely someone makes them?

Square RC do, but they’re quite expensive. 

T2shop.de do a decent range

I get a lot of hex/machine screws from accu.co.uk, though not sure if they do they hex/tapping combo 

[KEV THE REV]

On 1/30/2021 at 5:50 PM, Hobgoblin said:

I lean towards tapping for m3 where I can and using button

I do like button heads , less obvious and good clearance if you need it

[Juhunio]

15 minutes ago, NulnOilTycoon said:

I guess another question would be why on Earth can't you get m3 stainless steel, titanium, etc. tapping screws with hex fittings?  Surely someone makes them?

Square RC do, but they’re quite expensive. 

T2shop.de do a decent range

I get a lot of hex/machine screws from accu.co.uk, though not sure if they do they hex/tapping combo 

[NulnOilTycoon]

Just now, Juhunio said:

Square RC do, but they’re quite expensive. 

T2shop.de do a decent range

I get a lot of hex/machine screws from accu.co.uk, though not sure if they do they hex/tapping combo 

Interesting, I'll have to check them out.

[KEV THE REV]

1 hour ago, nowinaminute said:

drilled the hole to 2.5mm first? Might give it a try.

I usually drill 2.5 and hand tap - 3 steps for closed end or 1 step for a pass thru . I have used a drill tap for a pass thru plastic / alu. and worked out ok .

[nowinaminute]

44 minutes ago, NulnOilTycoon said:

I guess another question would be why on Earth can't you get m3 stainless steel, titanium, etc. tapping screws with hex fittings?  Surely someone makes them?

I've got some from Aliexpress. In A2/304. Quality probably not the greatest but better than the zinc plated mild steel ones lol. Haven't had any issues with them so far.

I think you can get 10.9 or 12.9 too.

[rich_f]

3 hours ago, NulnOilTycoon said:

I guess another question would be why on Earth can't you get m3 stainless steel, titanium, etc. tapping screws with hex fittings?  Surely someone makes them?

Back when I used to race my top force (early 2000's) I bought a titanium screw set for it from some place in Hong Kong like rc mart or Stella models, and it included all the correct tapping screws with button heads, except with hex sockets - a really nice set and they weren't even that expensive, can't remember the brand, if any. I just had a look but can't find them anywhere now.

[BruiseWayn]

the short answer is; if ABS, just use the self tapping screws. its too brittle for machine screws; threads r too fine.

[Krustybus]

This goes against everything I understand! Using machine screws in plastic...greasing them to get them in? sounds crazy to me lol. 

I guess it's more to do with my background of engineering construction machinery so it doesn't fall apart! For screwing into plastics in most cases use a moulded in brass insert...bit cost prohibitive on a model car! We do use Taptite thread forming screws in some limited applications. The biggest concern is generally parts vibrating loose so need to be careful with torque settings. 

[IoWBasher]

 

Not to upset anyone but all I can say is I've never had a problem using machine screws into plastic, other than sub par hardware and then that's the head that rounds out. On the rare occasion I've used grease to help facilitate cutting a new thread in hard plastics, but I never pre tap plastic holes. Works for me 

Most rc car manufacturers (Losi, Traxxas, Associated to name a few) use machine hex head screws, can they all be wrong ?

Furthermore even Tamiya use a machine type thread into plastic for king pins, ball ends etc.

[nowinaminute]

5 hours ago, Krustybus said:

For screwing into plastics in most cases use a moulded in brass insert

You can get them for quite a good price these days either the type you insert with heat or the helicoil ones you drill the hole and thread the insert in but it would still be fairly costly and time consuming to do a whole car.

I've used them many times for steering uprights though where the screws have a habit of backing out mid run, especially stuff like TL01, GF01, WR01 etc. Also used them in stuff where parts availability is low such as Nikko Dictator. Not much to lose when the threads are all stripped out anyway! I find the inserts to hold very securely in the plastic and you can use a little dab of blue threadlock and undo the screws again with no issues. It has totally eliminated escaping upright screws for me.

[Mechanic AH]

Just wanted to updated interested folks. So I ended up buying a few screws from McMaster to see what they look like and where they're made (Taiwan) before I buy bulk and they arrived today. Also, I've been asking about angle (head) on countersunk screws/holes and no one has yet to tell me the exact angle (forums or FB group). I wouldn't have asked if McMaster didn't provide angles as options .  I was just worried I'd buy hundreds for a number of screw lengths and they don't sit flush.

For the metric/M3 screws, I ended up referencing the screw diagram on Tamiya manuals and comparing it McMaster's diagram. So far it worked. I didn't get M4 screws and don't know if Tamiya uses the same 90 degrees. There was some ridiculous answer on an FB group and the person said 120! That's like almost flat. Sometimes I have to take FB answers with a grain of salt.

I've been debating from an aesthetic perspective if I want to go with all black stainless or bare metal stainless. The problem with black stainless is it's quite expensive almost between US 50 cents to over $1 per screw. Whereas plain stainless can go as low as 4 cents each. Then there is alloy steel which is nearly twice as strong (head would last long from maintenance) as stainless but probably less corrosion resistant. Comes in black oxide and blue dyed zinc. Zinc is out because they don't have some of the lengths I need. Anyway, I thought I'd get black alloy oxide for strength but now seeing bare stainless, I'll end up going with it. Attaching a photo with 3 types of hex flat/countersink screws (stainless, black oxide alloy, Tamiya dark JIS) and button (Tamiya JIS tapping screw, hex black oxide alloy, hex stainless).

 

 

[nel33]

Do the JIS?? Machined screws with hex heads  require a lock nut for them to be fully installed? I got some aluminum shocks for the TT02 that have hex machined screws 10mm long with sleeves. I don't think the Tamiya shock ball mount is compatible with the new shocks, they work great for Tamiya CVA. The support itself is 10mm thick where the self tap ball mount goes into and the hole doesn't pass through the other side. Does it simply screw into the plastic or do I need to get longer bolts, lock nuts and drill through the support? The eyelt itself takes up 5mm of length.