Drill size for 5.5mm self tappers

[Flyboy]

7 minutes ago, frangar said:

Yes but if the holes are already 4.5mm.......

Sorry mis read it, I thought he wanted to use M5 bolts.

[Flyboy]

8 minutes ago, Sir Nibble said:

It's 5mm plate, that's six and a half threads, ample.

Yes but there still won't be much thread depth,

[Sir Nibble]

31 minutes ago, Flyboy said:

Yes but there still won't be much thread depth,

Bet you couldn't strip it with a screwdriver.

[David Mack]

I have successfully tapped M5 threads in 3mm steel plate using a 4.5mm drill and a cheap M5 taper tap I bought years ago. I have used brass machine screws, so I don't overtighten then, but it has all worked out fine.

Now where can I get a titanium coated 4.2mm drill bit to do it properly next time?

[blackrose]

1 minute ago, David Mack said:

I have successfully tapped M5 threads in 3mm steel plate using a 4.5mm drill and a cheap M5 taper tap I bought years ago. I have used brass machine screws, so I don't overtighten then, but it has all worked out fine.

Now where can I get a titanium coated 4.2mm drill bit to do it properly next time?

 

eBay

[Chris Lowe]

You can get self drilling self tapping screws.

 

This one is for light section steel/aluminium

 

 

This one is for heavier section steel.

 

 

You can get these capable of self drilling and tapping anything upto 12mm thick steel.

[blackrose]

Thanks but they're not really suitable for brass pole and plank racks. Not countersunk for starters. They look more like roofing screws.

 

Having just drilled some small holes into my 5mm roof I'd be a bit dubious about trying to "self drill" those things through 12mm thick steel.

Edited June 18, 2020 by blackrose

[dmr]

A lot of stuff on our boat is m5 but m6 is nicer. The good thing about m5 is that you can just about drill and retap  to m6 if it goes wrong.

m6 is just about ok into 4mm steel, so as Blackrose has a 5mm roof it will be fine. I quite like stainless socket head bolts/setscrews for boat stuff.

The critical thing with cutting threads is a bit forward then a bit backwards to clear the debris out of the tap, this really is essential as breaking a tap is a very bad thing.

 

Something similar to this is a nice thing to have on a boat:..............

 

https://www.zoro.co.uk/shop/cutting-tools/combination/m3-m12-hss-tap-and-drill-set-28pce/p/ZT1132687X?utm_source=google&utm_campaign=pla%2B|%2BCutting Tools&utm_term=ZT1132687X&utm_medium=pla_css_1&mkwid=Eg6ya5W7-dc&pcrid=377670179276&pkw=&pmt=&prodid=ZT1132687X&slid=&pgrid={groupid}&ptaid=pla-392320859222&gclid=Cj0KCQjwoaz3BRDnARIsAF1RfLdvj3WxbPgYgt7cCTJsQeFI_tAcys2TiHN2zjcX8CMUtTl6KpSQFI8aAp3zEALw_wcB

 

Avoid the really cheap stuff that is only good for thread repairs and not up to cutting new threads in steel, but you don't need to pay mega money for full engineering/machine shop grade stuff.

 

...............Dave

[Murflynn]

I always use a temporary steel wood screw, self-tapping screw or machine screw before inserting a permanent stainless screw of the same size into any material.   Stainless is too soft and either snaps or the slot gets mashed.        

[WotEver]

6 hours ago, dmr said:

Something similar to this is a nice thing to have on a boat:..............

 

https://www.zoro.co.uk/shop/cutting-tools/combination/m3-m12-hss-tap-and-drill-set-28pce/p/ZT1132687X

Thanks for the link (I shortened it for you)

[Chewbacka]

As cheap taps snap easily leaving a blocked hole and good taps are expensive, you could buy the setting tool and use rivnuts.  I like rivnuts.

Edited June 20, 2020 by Chewbacka

[frangar]

29 minutes ago, Chewbacka said:

As cheap taps snap easily leaving a blocked hole and good taps are expensive, you could buy the setting tool and use rivnuts.  I like rivnuts.

Do rivnuts work in 5mm steel? I thought they were only good for thin panels? 

[BEngo]

Rivnuts are good, till they slip and spin.  Then they are a b**t*rd to drill out because the rivnut just goes round and round on the end of the drill.

They are available for thick material as well as thin, but, as always, you need to buy the right ones for the job in hand.

 

N

[Tony Brooks]

19 minutes ago, BEngo said:

Rivnuts are good, till they slip and spin.  Then they are a b**t*rd to drill out because the rivnut just goes round and round on the end of the drill.

They are available for thick material as well as thin, but, as always, you need to buy the right ones for the job in hand.

 

N

 

Exactly why I would never use them on my boat. too much experience of them and similar on vehicles!

[Chewbacka]

10 hours ago, frangar said:

Do rivnuts work in 5mm steel? I thought they were only good for thin panels? 

Yes, but you need the long type, and if you drill the hole the correct size and put a smear of epoxy around the head, they don’t spin or leak.  

[frangar]

9 hours ago, Chewbacka said:

Yes, but you need the long type, and if you drill the hole the correct size and put a smear of epoxy around the head, they don’t spin or leak.  

That’s interesting..the tooling seems to have come down a lot since I last looked quite a few years ago as well...I guess thanks to China & eBay although I suspect you get what you pay for like most things. 

[Cal Ando]

Just looked this up and the 4.2mm would suit m5 x .8 coarse thread.   A 4.5mm tapping size would suit an m5x0.5 find thread.   either way, there is only 12 thou difference between 4.2mm & 4.5mm = 6 thou variation in thread depth (per side)   The thread depth for M5 is 1mm = 40 thou so still loads of meat there.   As for the metal thickness, the pitch is 0.8mm, so you would have 5 threads in a 4mm thick plate, again loads of grippy stuff.   If it's for the pole racks, there's no shear or sideways force on it to speak of so again, should be fine.

Keep the 4.5 mm holes and tap with a 5mm taper, then a second tap, and all should be fine.  if it strips (it won't) you can still open it up to 6mm and the stripped hole will be correct tapping size of 5mm!

Alternatively you could use a PROPER screw thread like a UNF thread!   None of this modern, foreign rubbish!

 

[blackrose]

Thanks but too late! I've already drilled the holes out to 5mm and ordered a 6mm tap set.

[Sir Nibble]

5 hours ago, Cal Ando said:

Just looked this up and the 4.2mm would suit m5 x .8 coarse thread.   A 4.5mm tapping size would suit an m5x0.5 find thread.   either way, there is only 12 thou difference between 4.2mm & 4.5mm = 6 thou variation in thread depth (per side)   The thread depth for M5 is 1mm = 40 thou so still loads of meat there.   As for the metal thickness, the pitch is 0.8mm, so you would have 5 threads in a 4mm thick plate, again loads of grippy stuff.   If it's for the pole racks, there's no shear or sideways force on it to speak of so again, should be fine.

Keep the 4.5 mm holes and tap with a 5mm taper, then a second tap, and all should be fine.  if it strips (it won't) you can still open it up to 6mm and the stripped hole will be correct tapping size of 5mm!

Alternatively you could use a PROPER screw thread like a UNF thread!   None of this modern, foreign rubbish!

 

UNF is foreign. American.

[Phoenix_V]

1 hour ago, Sir Nibble said:

UNF is foreign. American.

we've still got the British Standared Whitworth though, still used on pipe fittings throughout the world

[BEngo]

The UN series were a wartime joint standards agreement  between the UK, Canada and the US , to ensure interoperability of war materiel. 

N

Edited June 22, 2020 by BEngo

[Tacet]

42 minutes ago, BEngo said:

The UN series were a wartime joint standards agreement  between the UK, Canada and the US , to ensure interoperability of war materiel. 

N

United Nations Fread

[Cal Ando]

 

1 hour ago, Tacet said:

United Nations Fread

UN = unified not United Nations!'

 

1 hour ago, BEngo said:

The UN series were a wartime joint standards agreement  between the UK, Canada and the US , to ensure interoperability of war materiel. 

N

As Bengo says: "In 1948, Britain, the USA and Canada agreed on the Unified thread as the standard for all countries that used inch imperial measurements. This was a combination of the best of the Whitworth thread form the rounded root to improve fatigue performance and the Sellers thread 60-degree flank angle and flat crests."   

https://www.fastenerdata.co.uk/threads#:~:text=In 1948%2C Britain%2C the USA,flank angle and flat crests.

Interesting as I thought it was a war effort as well.

This has flat crests and I prefer well rounded crests with my screws, personally!

[Man 'o Kent]

If you are into a bit of DIY like this first go buy a little  "ZEUS" book, everything you are  likely to need is in there and only 6" x 3" x 1/4" so it don't take up much space.

 

If drilling by hand, (including an electric drill), always drill a pilot hole first followed by a drill a tenth or two of a millimeter smaller than the required size and then finish with the final size drill. You will that way finish up with a hole that is more round and straight. Always use a lubricant, (down Mabel), even a smear of cooking oil is better than nothing but small tubes of specialist lubricant are available.

 

Always make sure the drill tip has a good sharp even point. Here I am lucky being a 'sinister', (left handed), I've lost count of the number of right handers that I've instructed on how to do it the "wrong way", if you don't tell 'em they don't notice!

 

The action is all in the wrist, a right hander will tend to use their right hand to move the drill against the grinding wheel and will get in a right old mucking fuddle. The trick is to use the right hand to support the drill bit and the left to do the down/rotate movement, easy to demonstrate, hard to describe!

 

Equally important is that each flute has an equal cutting edge if the drill is to cut to size. Here the Mk.1 eyeball comes into its own, held up to a strong light and shaded very small errors are easily seen and corrected.

 

[Machpoint005]

2 hours ago, Tacet said:

United Nations Fread

 

55 minutes ago, Cal Ando said:

UN = unified not United Nations!'

 

Unifed Fine, as opposed to Unified Coarse (UNC).

Both the work of the devil. Metric threads every time for me - at least then you can always tell whether A is bigger or smaller than B!