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skom25

To Tap, or not to Tap. That's the question!

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Hi,

I read many Topics but have not found satisfying answer.

I want to use Tamiya 54232 Thread Forming Tap and use machine screws.

Why?

I like hex machine screws. They are super cheap and available in many lengths.10 self tapping screws from Tamiya costs about the same as about 50- 100 good quality stainless machine screws.

Sounds good but I still have doubts.

1. Self tapping screw has much higher thread which probably cut into plastic better. Machine screw thread is tiny. I have feeling that at least in theory, it will be much easier to strip threads.

2. Tension. Machine screw needs to be tensioned to stay in place. Using it in plastic it is not possible to do. Is this not an issue in real world?

3. Holes diameter. I read that in low end models, holes are sometimes out of spec. What in that case?

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25 minutes ago, skom25 said:

1. Self tapping screw has much higher thread which probably cut into plastic better. Machine screw thread is tiny. I have feeling that at least in theory, it will be much easier to strip threads.

It is easier to strip threads than with a self tapper, but it's also easy enough not to. The only car I have with stripped threads is a second hand one that came with machine screws and harder plastocs as standard anyway, so I think it only really happens if someone has a tendency to overtightened. But the softer plastics would strip easier. Actually I have overtighted a couple of machine screws in soft plastic on tamiya but it's just TT-02/XV bumper - probably shouldn't use electric screwdriver on those soft plastics. DT-03 (my first) I went for hex self tappers. 

25 minutes ago, skom25 said:

2. Tension. Machine screw needs to be tensioned to stay in place. Using it in plastic it is not possible to do. Is this not an issue in real world? 

I think you're right but also that it's not an issue in the real world. I have had them loosen on occasion but only so far as they needed nipping up on a bolt check after many runs. 

25 minutes ago, skom25 said:

3. Holes diameter. I read that in low end models, holes are sometimes out of spec. What in that case?

I haven't experienced this but I guess you could always fall back on a self tapper. 

Overall, I mainly use them because I strongly prefer hex, but I also like just to use common hardware, so hex machine screws doing everything just works, generally. 

I note Optima Mid uses (hex) self tappers quite a lot, which I guess is for a little more strength, but when Tamiya spec hex they seem to spec machine screws. So maybe strong enough is strong enough. 

 

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I generally always tap holes when the instructions indicate putting machine screws into plastic (Such as the screws holding in the hotshot mechanism box).  Cutting threads makes it a doddle putting the screws in (I remember struggling not to round off the heads on the machine bolts on my OG hotshot when putting the mechanism box retaining screws in) and you can easily feel when they go tight. Another reason to reduce pressure on the plastic part you're threading into. Putting a machine screw into a non threaded hole puts a lot of outward pressure on the plastic. Hence why most second hand OG hotshot series cars have splits around the ball joints on the front steering uprights. Cutting a thread in the holes relieves the pressure on the plastic.

That's my 2 cents :)

 

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1 hour ago, skom25 said:

3. Holes diameter. I read that in low end models, holes are sometimes out of spec. What in that case?

Yes, I had came across that mainly for M2.5 screws on my Carisma. In that case, a tap is definitely needed and not a 54232. A tap removes materials while a thread former presses the thread in. The tap helps to open the too small hole up while it maybe impossible to get a thread former in due to the hole being too small. Since it is already too small to begin with, it is ok to remove some.

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5 hours ago, skom25 said:

2. Tension. Machine screw needs to be tensioned to stay in place. Using it in plastic it is not possible to do. Is this not an issue in real world?

That's true but only in metal on metal applications, even tapped plastic will hold screw just like nylon lock nut at least for first few assemblys

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I've been using machine head hex screws on all of my models for literal years without issue and I don't even own a tapping thread.

On higher-end models with Tamiya's carbon-reinforced plastics (lighter grey, mottled-effect plastic) this is recommended because the material is much harder. I have a few models with parts which are made from this material and whilst I don't condone it, I had no issues not tapping the threads first. Using a steel machine screw will cut its' own thread anyway. Going in dry for the first time (oo-er) will cause an almighty squeaking / creaking noise which isn't very nice. I've found a dab of plastic grease (moly / kit grease) helps cut the threads and stops this excruciating noise.

When I used to repair customer models in the shop it was very common to see stripped plastic threads. This is on your entry-level stuff; DT-02s, TT-01s, TL-01s etc. Folks were using the kit self-tappers but not realising where the bite point was, subsequently over-tightening them and ruining the part. We'd have to explain to them that they could either try the cyo glue option (coat the hole in glue then immediately put the screw in - with all the pitfalls you can imagine that brings) or buy a new parts sprue. Occasionally you'd be accused of deliberately "upselling" them parts they didn't need, because aesthetically the plastics look fine, but you now have a hole with a diameter larger than the M3 self-tapping thread, so it barely stays in or works loose.  

With machine screws, without tapping first, I find that feeling that initial "bite" point when the screw is all the way home is much, much easier with a large-handled 2mm hex driver than with the kit screws.  

This makes logical sense because you'll get more turns on a machine screw than a self tapper used in the same scenario, since the threads are much closer together so it's tightening less with each full turn than the self-tapper would. The kit screws have this very vague feeling when fully-tightened, which encourages people to 'nip it up another turn' and immediately wreck the plastic. 

Proceed at your own risk, if you can call it that. There are more risks proceeding with the self-tapping screws!

One more tip-
The kit self-tappers last ~ 2mm of thread is doing nothing in 90% of cases. If you look at the screw it tapers right down (hence, self-tapper). A machine thread screw does not do this. On my vintage / older models when rebuilding them I use a screw 2mm shorter than prescribed - ie. 3 x 8mm machine screws in lieu of a 3 x 10mm self-tapper. 

I'm keeping my local hardware supplier in business with all the M3 x 8mm screws I order :lol:

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3 hours ago, ChrisRx718 said:

I'm keeping my local hardware supplier in business with all the M3 x 8mm screws I order :lol:

I used 180 M3x8 socket cap screws just to hold on the wheels on the War Rig.............

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9 hours ago, BuggyDad said:

It is easier to strip threads than with a self tapper, but it's also easy enough not to.

The trick to not ever strip a thread when you re-install the screw, be it self tapping or machine, is to first turn counter clockwise with gentle pressure until you hear the click, then start turning the screw normally (clockwise). If you didn't hear that click, you will likely butcher new threads over the existing ones... And it will strip in very short order.

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On 3/30/2023 at 11:59 AM, Pylon80 said:

The trick to not ever strip a thread when you re-install the screw, be it self tapping or machine, is to first turn counter clockwise with gentle pressure until you hear the click, then start turning the screw normally (clockwise). If you didn't hear that click, you will likely butcher new threads over the existing ones... And it will strip in very short order.

Great advice!!! I learned that the hard way with my TT-02 :lol:!

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15 minutes ago, RC_FunLand said:

Great advice!!! I learned that the hard way with my TT-02 :lol:!

On that chassis, the left/forward most screw of the spur gear cover has a tendency to strip very easily. The other place that needs attention when doing maintenance are the 2 screws holding the (stock) shock towers. These are difficult to align well and begging to strip inside the diff covers.

I now tap everything WITH GREASE and use machine threads only :)

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On 3/31/2023 at 4:44 PM, Pylon80 said:

On that chassis, the left/forward most screw of the spur gear cover has a tendency to strip very easily. The other place that needs attention when doing maintenance are the 2 screws holding the (stock) shock towers. These are difficult to align well and begging to strip inside the diff covers.

I now tap everything WITH GREASE and use machine threads only :)

I stripped out:

a) leftmost spur gear screw (it no longer stays in)

b) one bumper screw

c) one shock mount screw

 

Lol. Surprised we share similar problems!

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I've seen machine screws used in many places into plastic in this hobby. I usually tap the hole first if it is going into a place that is difficult to get the thread started.
In general machine screws into plastic are plenty strong enough for the job. You just have to be careful not to strip them. And....when I9 have stripped them I've often bodged them up but putting superglue or loctite onto the screw and putting it in.
It tends to work.

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On 3/30/2023 at 8:48 PM, ChrisRx718 said:

I've been using machine head hex screws on all of my models for literal years without issue and I don't even own a tapping thread.

Same here. The only model that have a few self-tap screws left is the CC-01. All the others are using machine hex screws and have never had an issue. 

On 3/30/2023 at 11:59 PM, Pylon80 said:

The trick to not ever strip a thread when you re-install the screw, be it self tapping or machine, is to first turn counter clockwise with gentle pressure until you hear the click, then start turning the screw normally (clockwise). If you didn't hear that click, you will likely butcher new threads over the existing ones... And it will strip in very short order.

This!

Learned this back in college when we were assembling an Aerospatiale Gazelle in one of our hands-on subjects in engineering. The team instructor taught us how to apply proper force with regular screws and the use of torque wrench for those that needed including nuts, bolts, machine and self-tappers. I've always applied it to my builds whether a 1:1 cars, bikes, RCs, turntable works, sound system installations, etc.  

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So, what is theory?

In a few days I will start to build TT-02B. I will use kit screws, but during rebuild of DT-03 I will try to use machine screws on new parts. I just do not want to ruin new model, if something will go wrong.

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I always use the kit screws or titanium self tappers from tamiya and have never had problems since i use the jis screwdrivers and stopped overtightening the screws. I do the counterclockwise-till-click thing, too. 

On some occasions ive even put Machine screws into existing self tap threads - e.g. on a ta03 when replacing the upper links of the suspension fastened with self tappers - with the hop up turnbuckles that sit on Ballenstedt with machine threads. Even tamiya doesnt suggest otherwise. 

When i know i will put Ball ends in though, to have adjustable turnbuckles, i Start off with Machine screws though. No tapping though, Just gentle with the tamiya jis screw driver,  and sloowly and straight. Even with a Pause in between cos of heat.... 

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I bought XV-01 and Tap. One thing that I am not sure. Should I tap to the bottom of the hole or leave 1 mm or 2 mm without thread?

@toyolien suggested to do this, probably to lock bolt a bit.

@matisse I saw that you tapped a lot. What do you think? 

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1 hour ago, skom25 said:

I bought XV-01 and Tap. One thing that I am not sure. Should I tap to the bottom of the hole or leave 1 mm or 2 mm without thread?

@toyolien suggested to do this, probably to lock bolt a bit.

@matisse I saw that you tapped a lot. What do you think? 

Yep. Made sense to me that the tap was used to start the thread as the reinforced plastic is so hard. Then the last 1/4 or so the bolt should cut so that its in a little tighter. In reality I don't think it would matter too much if you used the tap to form the full depth. 

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2 hours ago, skom25 said:

I bought XV-01 and Tap. One thing that I am not sure. Should I tap to the bottom of the hole or leave 1 mm or 2 mm without thread?

@toyolien suggested to do this, probably to lock bolt a bit.

@matisse I saw that you tapped a lot. What do you think? 

Yeah for me I like to leave enough untapped that it'll just hold onto the screw a little tighter. You don't need to leave much for this, maybe 2mm. Equally, I'm tapping mostly just to locate the screw nicely and make sure it'll always engage as intended on reassembly, which perhaps doesn't need that much to be tapped either. 

In short, I tap some but not all, I don't think it really matters how much. 

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Myself ... tapping over 20 years now. Since I discovered cracks around holes in my old Clod Buster chassis, where I used self-tappers (I was young and the model got quite bashed around). Every model I own/buy is getting tapped for machine screws where possible.

1. I like the look more than JIS screws. For scale models I even use screws with hex heads instead of socket head/allen screws. We have a good supplier here in Germany called Knupfer.

2. I am able to use screws that are longer than proposed by the manual, what I sometimes do where I believe the extra length and strength would be an advantage.

3. Tapping not all the way to the end of the hole is quite reasonable, as some here wrote, I do the same.

4. Sometimes I use a grub screw/bolt instead of a regular screw and use a nut to fasten a part (for example front gear lid on XC/CC01). Maybe added with some glue for the bolt itself (Don't ever use Loctite for screws in Tamiya plastic! - been there, done that).

You can argue a lot above that. But, for example, if you run a 1/16th scale Tamiya tank nicely painted and weathered and you have JIS screws visible everywhere ... well then something is screaming inside of me. I call it my inner Monk (You know the TV series?). At the end everyone must decide for himself if he wants to go "the extra mile". In general there should be nothing wrong about JIS screws, even though I don't like 'em. And I bought several old models with original screws stripped or jammed in close to breakage or both, what made me switch to a different type of screw. More control when tightening, less possibilities to strip a hex/socket head/allen screw in that scale. Maybe it's also due to the fact, that I eliminated slotted or phillips screws even in all other things I do in real life too.

Cheers

Martin

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On 3/30/2023 at 8:48 AM, ChrisRx718 said:

If you look at the screw it tapers right down (hence, self-tapper)

I know this is an old post, but "taper" and "tapper" are totally unrelated words and meanings:

- to "taper down" means that the diameter is larger at one end than the other, so the screw is referred to as "tapered" - this can also apply to many other objects, tapered drill bits for example

- "self-tapper" means that the screw taps its own threads as it screws into the hole

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I tap to the bottom, being careful to stop as soon as I sense the slightest increase in torque. This makes it easier to feel what I am doing when turning the screws in those threads later on since they feel the same until you are in the tightening stage.

One exception is when I make turnbuckles. I use the Tamiya tap for one side and a left-hand rolling tap for the other side of course, but I only tap the first two mm. Then I let the turnbuckle itself make it's own threads. This way the result is very straight and easy to do but doesn't come loose. Unlike regular screw attachments that you have to tighten, turnbuckles are left "loose" by design and so shouldn't be tapped as the way.

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9 minutes ago, Pylon80 said:

This makes it easier to feel what I am doing when turning the screws in those threads later on since they feel the same until you are in the tightening stage.

Good point!

9 minutes ago, Pylon80 said:

One exception is when I make turnbuckles. I use the Tamiya tap for one side and a left-hand rolling tap for the other side of course, but I only tap the first two mm. Then I let the turnbuckle itself make it's own threads. This way the result is very straight and easy to do but doesn't come loose. Unlike regular screw attachments that you have to tighten, turnbuckles are left "loose" by design and so shouldn't be tapped as the way.

I found my own method and turnbuckles are no longer issue.  

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3 hours ago, El Gecko said:

I know this is an old post, but "taper" and "tapper" are totally unrelated words and meanings:

- to "taper down" means that the diameter is larger at one end than the other, so the screw is referred to as "tapered" - this can also apply to many other objects, tapered drill bits for example

- "self-tapper" means that the screw taps its own threads as it screws into the hole

Sorry, not worded very well on my part. The Tamiya screws are tapered, with the thin tip facilitating that self-tapping-action. If they were the same 'girth' all the way along the threads would split the plastic pretty quick. Self-tapping screws have to taper (down to a point in the case of wood screws). 

 

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3 hours ago, Pylon80 said:

I tap to the bottom, being careful to stop as soon as I sense the slightest increase in torque. This makes it easier to feel what I am doing when turning the screws in those threads later on since they feel the same until you are in the tightening stage.

One exception is when I make turnbuckles. I use the Tamiya tap for one side and a left-hand rolling tap for the other side of course, but I only tap the first two mm. Then I let the turnbuckle itself make it's own threads. This way the result is very straight and easy to do but doesn't come loose. Unlike regular screw attachments that you have to tighten, turnbuckles are left "loose" by design and so shouldn't be tapped as the way.

Turnbuckles.

I found easy method. I have one, spare turnbuckle. I put small dot of silicone grease inside rod end, to make work bit easier. Then I hold rod end and which is most important, I use spanner to rotate turnbuckle. I screw it into turnbuckle, unscrew and screw again to make threads bit more loose.

I found that it is even better, to grab rod end using towel/ cloth.

Preparing set for whole car is about one hour. Then I can screw aluminium turnbuckles, without worries that I will damage them.

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49 minutes ago, skom25 said:

Turnbuckles.

I found easy method. I have one, spare turnbuckle. I put small dot of silicone grease inside rod end, to make work bit easier. Then I hold rod end and which is most important, I use spanner to rotate turnbuckle. I screw it into turnbuckle, unscrew and screw again to make threads bit more loose.

I found that it is even better, to grab rod end using towel/ cloth.

Preparing set for whole car is about one hour. Then I can screw aluminium turnbuckles, without worries that I will damage them.

If you ever try to make turnbuckles with taps, I can almost guaranty that you won't look back. But at the end of the day, the best way is whichever way works best for you.

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