Thread: Where to buy an 8-40 forming tap (or set)

I just bought some of these

https://reloadingdirect.co.nz/shop/g...ews-torx-head/

GunScrewsTorxHead-8-40 x 1/4" T15 Fillister


Some of the more astute readers may be able to correctly guess why I bought them. I won't be going into details or confirming or denying.

I want to buy the tap or taps required for these screws for tapping aluminum. Can anyone advise a good place to order online and which is the definitively correct tap to buy?

8-40 tap set via blackwood paykels, bay engineers, holmes industrial trade tools (or whatever the local trade tools is in your patch...). Get the three, starting, intermediate, bottoming, and also get a decent tapping lube product along with some kerosene.

Thanks No.3. The tapping lube and kero is a good tip too. Sorry if this is a dumb question but is this tap the correct thread with a different nomenclature?

https://www.bayengineerssupplies.co....-tools/1-8-unc

like how .223 and 5.56x45 are the same? And should I look for UNC or UNF or BSW or something else.

I want to get this right first time and not have to order from this catalogue - http://cdn.ebaumsworld.com/mediaFile...9/82462320.jpg

your link is 1/8 unc and I think is not the same as 8/40.
I use lots of taps but never come across 8/40,
This guy has 8/40 and maybe the same stuff you looking for,
https://tradetools.co.nz/shop/thread...econd-hand-tap

Else, visit your local engineer shop, usually, they are helpful and you can swap if you bought the wrong stuff.

Depends on how many threads you planning to do or how much you want to spend
I would start with just tapper or starting tap.

Originally Posted by Snap 4T

your link is 1/8 unc and I think is not the same as 8/40.
I use lots of taps but never come across 8/40,
This guy has 8/40 and maybe the same stuff you looking for,
https://tradetools.co.nz/shop/thread...econd-hand-tap

Else, visit your local engineer shop, usually, they are helpful and you can swap if you bought the wrong stuff.

Depends on how many threads you planning to do or how much you want to spend
I would start with just tapper or starting tap.

Thanks,
I will tapping four holes in aluminium. I will grab that one you have linked, but will need the 1st tap and a bottoming tap too.

I'd be cautious with forming taps, all the ones I've used produce quite a loose thread and a raised ridge around the hole. My preference is for cut taps but forming taps are stronger but do take a little more force to start.
I'll check my toolbox tomorrow but I'm not likely to have one.

If you're going to tap them in a machine try to avoid any taps with straight flutes (hand taps) as they block and break too easily, machine taps have spiral flutes that pull the swarf out the top of the hole or spiral point that push the swarf out the bottom of the hole (deep or thru holes only)

Originally Posted by No good names left

I'd be cautious with forming taps, all the ones I've used produce quite a loose thread and a raised ridge around the hole. My preference is for cut taps but forming taps are stronger but do take a little more force to start.
I'll check my toolbox tomorrow but I'm not likely to have one.

If you're going to tap them in a machine try to avoid any taps with straight flutes (hand taps) as they block and break too easily, machine taps have spiral flutes that pull the swarf out the top of the hole or spiral point that push the swarf out the bottom of the hole (deep or thru holes only)

I will just be tapping by hand, carefully. I hadn't heard of forming taps until I was searching the net to try and find out which type of thread standard I should use. It did occur to me that the forming tap might create swelling.

I may have used machine screws in the past as self form tapping screws and had noticed this happening.

When I was machining delicate parts I had to finish the face, D&T the holes then prog another finishing pass over the face due to the swelling. If the holes were close together they could crush the previously tapped hole.
With such an oddball thread you may have no choice as to what style of tap you get. As for lube thin liquids are best "Rapid Tap", "CRC", kero would all work well.

It's not an oddball thread, its a standard imperial size. It's just not common in NZ any more. An 8-40 cut thread is fine in this size, but be aware that you will be removing the anodizing "hard layer" which won't make the thread last as a factory one would. If the ridge from forming is an issue, hand countersink it with a drill bit to remove the ridge, easy as. To be fair, you are removing the anodizing when you damage the threads anyway so if you want to recover the rings you don't have a choice.

I thought 32 & 36 tpi were the standard, Is it a specialty optics thread ? I've never seen 8-40 even when working in the US

www.brownells.com is a good supplier.
6-48 and 8-40 are the most common sizes for scope base screw holes, 6-40 being the third size but not as common on the modern production.

Originally Posted by Friwi

www.brownells.com is a good supplier.
6-48 and 8-40 are the most common sizes for scope base screw holes, 6-40 being the third size but not as common on the modern production.

Yes, used on firearms in the US and not much else. I think Remington has gone to 8-40 on their Alpha?
GPM.

It's a struggle to get those taps here in nz, most of the clowns in the tool shops have never even heard of them and just stock std metric and coarse thread imperial.
Brownells USA is the best place to get these taps.
I have also purchased them from Murray at Avparts nz but cant recall if he had them in stock or imported them for me.
https://avparts.co.nz/

They are used in a lot of other things as well like US-spec diving gear - also some parts on certain US made bikes and motor parts. Also electronics and boat parts like control levers and some small pump fasteners so the size isn't that uncommon. Easier to buy the taps than the damn screws I thought! I got my last set from Bay Engineers off the shelf for what it's worth.