Author Topic: Tapping -- How to's and How not to's....  (Read 11860 times)

Offline Lew_Merrick_PE

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Tapping -- How to's and How not to's....
« on: August 05, 2010, 11:31:20 AM »
All,

I have seen several threads start to deal with tapping problems.  I am starting this topic to collect information in one place to ease searches for support in this arena.

I have a couple of thing posted at http://www.scribd.com/Lew%20Merrick that may be of interest to you.  One is the paper Pilot Hole Considerations which details how to calculate the size of tap drill you should use to provide a given percentage of full thread and how you can calculate the effect a change in the percentage of full thread will have on your joint.  Another paper, UN Thread Data Chart provides information on full thread strengths for most Unified National (inch-based) threads.  I have not done this for metric threads as there is still no single set of tolerances and allowances needed to complete the calculations for them.  Using the largest pilot (tap-drill) hole you can for any given task makes tapping a whole lot easier.  This is rule zero for tapping.

Rule one is to buy good quality taps.  The cheapie taps are cheap for a reason (in most cases).  They cost you dearly when trying to remove a broken one from a hole!  I am partial to OSG taps, but I designed and built some grinding machines for them years ago and can buy them direct from the factory -- which has something to do with my bias.

Rule two is to keep them sharp!  If you do not have the set-up (or access to a set-up) to sharpen them, be very careful as it is easy to make them worse trying to hand sharpen them.  When in doubt, throw it out.

Rule three is to be sure that you are driving them straight into your part.  Very few people have the hand strength to torque a (sharp) #10 (5 mm) tap to the point of breaking.  A six-year-old can break such a tap in bending very easily.  Tap guides are cheap at twice the price.  A Tapmatic type head is golden (and there's an inexpensive Indian-made head being sold by Harbor Freight and the like that is reasonably good so long as you disassemble it, clean up the burrs, lubricate everything nicely, and reassemble it -- I have seen them on sale for less than US$75 several times in the recent pass and I have "cleaned-up" three of them for friends in recent years).

Rule four is use the right lubricantTap-Magic Gold is my current favorite when dealing with obnoxious materials (hardened stainless, titanium, nickel alloys, etc.).  Moly-Dee is my more general purpose (steel) lubricant -- though I still use axle grease for plain carbon steels.  I use cetyl alcohol (wax) for most aluminum tapping (though Tap-Magic Aluminum works better on non-heat-treated aluminum).  I often use lard when tapping copper-based materials.  I usually tap cast iron dry.


Offline AdeV

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Re: Tapping -- How to's and How not to's....
« Reply #1 on: August 05, 2010, 12:07:59 PM »
Good stuff, thanks Lew.

Nothing about cleaning broken taps out with conc nitric acid though, I notice!  :lol:

Anyway.... a question: Can a TapMatic head be used with standard HSS taps? If not, what sort of taps does it need? I'll stump up the money for a TapMatic if it's going to take ordinary taps.
Cheers!
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Offline raynerd

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Re: Tapping -- How to's and How not to's....
« Reply #2 on: August 05, 2010, 01:21:54 PM »
I also have a question regarding tap drill sizes.

I have quite a collection of old drill bits, many handed down or been given with old equipment. These are virtually all imperial, the only sets I have purchased (except the odd odd-ball now and then) are the standard 1mm - 10mm metric set in 0.5mm increments. This means that when I want to tap a metric thread and my little Zeus chart for example it tells me I need a 3.3mm (or whatever, I haven`t the book to hand!) drill for a M4 tap,  I end up using the closest to. Now I use to use a 3mm drill but I was breaking taps because too much material was jamming them, however a 3.5mm drill doesn`t give you a full thread. I`ve lately been searching my imperial drills to find a closest too but it is still not ideal. So what do most of you guys do...in a home workshop, do you actually have a set of "most used" tapping drill sizes? - I`ve never actually seen a set for a sale and I`m guessing something like a metric tapping drill size set would be useful, I`ve never seen such a set but maybe I`m not looking hard enough!  Sorry if this seems obvious, I`m learning!
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Offline Stilldrillin

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Re: Tapping -- How to's and How not to's....
« Reply #3 on: August 05, 2010, 02:25:10 PM »
Chris,

I drill using the nearest 1/2mm sized drill.

Tapping size..... Say, 5.5mm....... I drill first 5mm, then drill again with 5.5 for best accuracy.

Tapping size..... Say, 5.7mm....... I drill hole with 5.5mm drill only.

Tapping size..... Say, 5.9mm...... I drill first 5.5mm, then drill again 6mm, for nearest size.

Works for me!  :thumbup:

David D
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Still modifying bits of metal... Occasionally, making an improvement!

Offline Bluechip

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Re: Tapping -- How to's and How not to's....
« Reply #4 on: August 05, 2010, 03:36:55 PM »
Chris

Get some of these,... in 0.1 mm increments ..

http://www.axminster.co.uk/axminster-packs-of-5-ground-hss-drill-bits-prod20559/

Use the correct size, or the one you want anyway.   :lol:

For the price, these ain't bad drills, certainly better than some I've had ..

Dave BC
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Offline j45on

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Re: Tapping -- How to's and How not to's....
« Reply #5 on: August 05, 2010, 03:43:43 PM »
Arc Euro Trade also have small drill packs in 0.1 mm increments these ones are TiN coated but a little dearer
I have the 1-10mm set and they are not bad drills

http://www.arceurotrade.co.uk/Catalogue/Cutting-Tools/Twist-Drills/Drill-Bits---TiN-Coated
Jason

Offline Tinkering_Guy

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Re: Tapping -- How to's and How not to's....
« Reply #6 on: August 05, 2010, 03:51:50 PM »
This is an excellent reference: http://littlemachineshop.com/Reference/TapDrillSizes.pdf.  It covers metric and Imperial screw and drill sizes, and also allows for the type of material being worked.
Tinkering_Guy
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Offline j45on

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Re: Tapping -- How to's and How not to's....
« Reply #7 on: August 05, 2010, 04:05:48 PM »
This is an excellent reference: http://littlemachineshop.com/Reference/TapDrillSizes.pdf.  It covers metric and Imperial screw and drill sizes, and also allows for the type of material being worked.

Thanks thats getting printed and laminated and going in my shop  :thumbup:
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Offline Lew_Merrick_PE

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Re: Tapping -- How to's and How not to's....
« Reply #8 on: August 05, 2010, 04:31:49 PM »
Nothing about cleaning broken taps out with conc nitric acid though, I notice!

We can revisit it if you like, I only opened the door.

Anyway.... a question: Can a TapMatic head be used with standard HSS taps? If not, what sort of taps does it need? I'll stump up the money for a TapMatic if it's going to take ordinary taps.

Yes, I use my TapMatic with HSS taps all the time.  The main thing it to match the tapping rotational speed properly.

Offline AdeV

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Re: Tapping -- How to's and How not to's....
« Reply #9 on: August 05, 2010, 06:49:42 PM »
Nothing about cleaning broken taps out with conc nitric acid though, I notice!

We can revisit it if you like, I only opened the door.


No... I was only kidding, hence the smiley...

Anyway.... a question: Can a TapMatic head be used with standard HSS taps? If not, what sort of taps does it need? I'll stump up the money for a TapMatic if it's going to take ordinary taps.

Yes, I use my TapMatic with HSS taps all the time.  The main thing it to match the tapping rotational speed properly.

I'm looking at maybe purchasing a 50TC/DC unit. If I wanted to tap M6 in aluminium to a depth of 2", would this device do the job - and what sort of speed will it tap at? The website blurb says it has a "re-entry cushion" to prevent cross-threading; which suggests to me I can plunge multiple times (maybe with taper, 2nd & plug?) into the same hole & it will find the threads & augment them, rather than chewing a new set out of the old...

e.g. here's a utoob video which seems to suggest a tapmatic will scorch through metal:

http://www.youtube.com/watch?v=W_tkCZgNutI

Thoughts?
Cheers!
Ade.
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Offline Lew_Merrick_PE

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Re: Tapping -- How to's and How not to's....
« Reply #10 on: August 06, 2010, 11:45:42 AM »
I'm looking at maybe purchasing a 50TC/DC unit. If I wanted to tap M6 in aluminium to a depth of 2", would this device do the job - and what sort of speed will it tap at? The website blurb says it has a "re-entry cushion" to prevent cross-threading; which suggests to me I can plunge multiple times (maybe with taper, 2nd & plug?) into the same hole & it will find the threads & augment them, rather than chewing a new set out of the old...

You main problem in tapping 2" (50 mm?) deep with an M6 tap will be getting a tap with that ability.  You will need to use an "extended, undercut" tap to do the job.  You may need to make (or buy) an adapter to allow your head to hold a reduced shank tap.  I do this quite commonly with taps as small as #6.

I typically run my head for aluminum with a spindle speed of 240 rpm (this is the input speed, the head I have reduces that by 30% through the planetary gearing) for taps #10 and larger.  I will slow it down to as low as 80 rpm for small taps and/or alloy steel.  If you want speed of process, use a fixed head drive with a clutch release and use thread forming taps.  The TapMatic is faster and more consistent than hand tapping -- and saves your wrists.

Yes, you can "re-enter" holes easily.  When the tip pressure reverses the direction (to clockwise -- by lifting the planet to the "drive-in gears"), you hold the tap at the "entry height" for a couple of revolutions and the tap will "grab" the existing threads.  This is handy when tapping deep holes as you can remove the tap from the hole, clean off the swarf, add another dose of tapping fluid, and continue on.  As I have hit the age when aspirin is my drug of choice, I will set-up my tapping head for as few as three holes...

Offline ven

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Re: Tapping -- How to's and How not to's....
« Reply #11 on: October 07, 2010, 04:44:52 PM »
Just to agree with what others have said.
Try to obtain sets of imperial drills, 1mm to 6mm (?) sets in 0.1 increments, metric ones in 0.5mm increments, letter drills and number drills.  The good ones aren't cheap but they will last for years if you are careful.  Don't go for cheapness, no matter how tempting.
It took me years of Christmases and Fathers' Days to get all of mine, but it is really good to be able to just reach out and pick up any size drill, up to about 1/2"/12.5mm.
The next phase is to have a set or sets with the tips hand-ground slightly for work on brass, which tends to grab.

Offline Jonny

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Re: Tapping -- How to's and How not to's....
« Reply #12 on: October 07, 2010, 06:37:12 PM »
Theres a lot of rubbish drills out there probably made in China with German sounding names on and you may think you are getting a bargain.

I do a lot of hand tapping with aluminium 6082 T6 usually M3 and M4 in at 15 degrees. Found quality HSS tend to grab and pick up more than cheap carbon types. Now i have the last 6 months changed over to the machine taps with coloured bands ie red top, yellow top etc to suit the material. Plough straight in, no backing off.

When i need accurate tapped holes i usually use one of the mills. Lock beds up, drill hole to correct size, change to decent tap, drop speed usually lowest, oil and use same way as Tapmatic except when at bottom hit reverse. Everyone a gem from M5 to M20 too scared at anything less than M5.


Offline Lew_Merrick_PE

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Re: Tapping -- How to's and How not to's....
« Reply #13 on: October 08, 2010, 11:47:54 AM »
The good ones aren't cheap but they will last for years if you are careful.  Don't go for cheapness, no matter how tempting.

My daughters (who grew up working in the shop with me) heard my swearing as I tried to find the drill set that had hidden itself on me about 20 years ago.  They saved their pennies and bought me one of the ultra-cheap tri-dex (number, letter, & fractional) drill bit sets.  It sat proudly on a shelf in my shop for several years before my youngest daughter asked me why I wasn't using them.  I let her try to drill a hole with them.  She was aghast at the results (which resulted in a lesson about measuring roundness and straightness of drill bits).

Most major manufacturing operations do not sharpen drill bits, they just scrap them when they get dull.  If you can find the "surplus yard" they sell to, you can pick up otherwise very high quality (but now dull) drill bits for a fairly small fee (I paid $0.50/lb a couple of years back).  Take a micrometer with you.  My daughters now have their own tri-dex sets filled with good quality drill bits.  It has now become a family tradition that my grandkids get a tri-dex drill set for their 12th birthday.  The tri-dex cases far out-cost the bits!

I paid about $100 for my first set of cobalt-HSS drill bits (in three separate indexes) back in 1968.  I still have them and they work fine.  I picked up a broken Lysle drill-bit grinder shortly thereafter.  (I rebuilt it and it too works fine.)  I got a Darex drill-bit sharpener some years back.  That is what I use for most "touch up" drill-bit sharpening and only break out the Lysle when I need to completely rebuild the point.  I have made a set of wooden "bins" for dull bits and another for "sharpened, ready for service" bits so I don't have to stop and measure them when I have dulled a bit.  Excepting my first set of bits, I don't think that I have paid $25 for all the bits in my shop -- which currently sits at (5) tri-dex sets (one for each major machine), (2) ground short as "screw machine" bits, (2) spare tri-dex sets (so I have one to grab when I have to work in someone else's shop), matched "drill & tap" and "drill & ream" sets each in their own wooden stand, and "spare bits" for standing ready to be pressed into service when another bit gets dull.

The "set" my daughters bought me have been recycled into scriber points and the like.  My youngest daughter has the tri-dex case (now filled with good bits) she and her sister bought me for Father's Day back in the early-1990's.
« Last Edit: October 08, 2010, 11:50:09 AM by Lew_Merrick_PE »

Offline cidrontmg

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Re: Tapping -- How to's and How not to's....
« Reply #14 on: October 08, 2010, 05:21:28 PM »
Heh, Lew, I´ve done a very similar thing. I bought some time ago a drill set that goes from 1 to 10 mm in 0.1 mm steps. It actually came in 2 metal cases. I bought it not for the drills - I tried some of them, for fun, full well anticipating the result, and couldn´t decide if I should cry or laugh - but for the cases. They´re reasonably well made, the holes are quite accurate, there´s enough space for even a bit longer drill bits, etc. Since then I´ve repopulated the cases with the best quality bits I´ve been able to get. The drills in those cases are sort of a last recourse, I use them when I want a hole exactly the size. For run of the mill drilling, holes that are usual sizes for screw clearance, tapping, etc., I have a small set of also first class drills, that I buy in lots of 5 to 10 bits.
Drill sharpening is still a bit of a problem, especially below 5 mm. But for the price of a commercial drill sharpener, I can buy an awful lot of small drills, so it´s not a big deal. Sharpening milling cutters would be a far greater priority, also so far unsolved... :offtopic:
 :wave:
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Offline Powder Keg

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Re: Tapping -- How to's and How not to's....
« Reply #15 on: October 09, 2010, 12:00:27 PM »
Over the years of hand taping I've noticed why most  taps  get  broken. The  person is simply not paying attention to the job at hand. They are looking around the shop, chatting with  a buddy, Or  whatever. If you are watching the tap and paying attention to what  you are doing. You wont shouldn't them. I've done a bunch of 0-80 with  just a hand held T-handle and never broke one. Knock on wood

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Offline Lew_Merrick_PE

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Re: Tapping -- How to's and How not to's....
« Reply #16 on: October 09, 2010, 01:04:58 PM »
I've done a bunch of 0-80 with  just a hand held T-handle and never broke one.

Wes, you aren't trying!  I was tapping holes in a missile simulator body (.7500-10UNC) when the (8500 lb) bar started to roll (after being hit by a forklift).  I snapped off the tap while trying to keep the body from rolling.  I did, however, succeed in getting my foot and leg out of the way...

The vast majority of the time I break a tap, I am trying to get one more hole threaded with a known dull tap.  Yeah, stupid but we all reach that point.  More taps are broken by bending than torsion.  You have to be a weight lifter or a rock climber to break a #10 tap by hand with torsion.  A 6 year-old can snap a 3/8 inch tap in bending (my grandson proved this a few years back).  Paying attention is the key, but you can't always "win" that way...

Offline Mike E.

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Re: Tapping -- How to's and How not to's....
« Reply #17 on: May 24, 2017, 01:34:14 PM »
Reading this old thread I thought I would add my 2 cents worth about tapping aluminium. Consider using "Lacquer Thinner" as a cutting fluid. Many years ago I learned this trick from an old machinist who worked at Lockheed Aircraft. I've tapped holes as small as 2-56 with excellent results.
Mike

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Offline sparky961

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Re: Tapping -- How to's and How not to's....
« Reply #18 on: May 24, 2017, 04:12:41 PM »
Reading this old thread I thought I would add my 2 cents worth about tapping aluminium. Consider using "Lacquer Thinner" as a cutting fluid. Many years ago I learned this trick from an old machinist who worked at Lockheed Aircraft. I've tapped holes as small as 2-56 with excellent results.

What's the logic in this? Maybe it stays liquid in a really small hole but for any "normal" size it will have evaporated long before having the chance to be helpful.

There are plenty of "old machinist's tricks" like this you hear about, but a commercial cutting oil designed for the job is often the best solution.

Offline PekkaNF

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Re: Tapping -- How to's and How not to's....
« Reply #19 on: May 24, 2017, 05:53:11 PM »
I may be going against the flow, but I don't constantly back off when hand tapping, certainly not the 1/4" turn routine. My reasoning is that because it is universan acepted fact the when you ream: don't back off - you chip the cutting edge. I beleive there is some extent same mechanics totapping too. I may ease a small fraction of the turn on very difficult material, just to assit swarf packing.

incidently I used some time to get boxes and organisize my tapps. The big idea is to keep one thread size (metric coarse) tools on one box: Taps, tapping size drills (by 10 each size, short), clearance hole drill, countersunk bit and recess bit.

Too some time to design the apropriate sticker, nicked the graphics and all information from three sources.

Boes will stack two high, or I could nest them two rows, two high, but I'm using bigger box to accomondate reamers and their drills and one box for nonstandard taps.

M10 and biger stuff will go on bigger boxes on bigger sellf.

Pekka

Offline PK

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Re: Tapping -- How to's and How not to's....
« Reply #20 on: May 25, 2017, 12:33:33 AM »
I'm a big fan of spiral flute taps and torque limited electric drivers. You have to work hard to break a tap with that setup and seeing the swarf curl up out of the hole in three contiguous strips makes me happy....

Offline awemawson

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Re: Tapping -- How to's and How not to's....
« Reply #21 on: May 25, 2017, 02:22:13 AM »
I'm with PK on this. I now only buy spiral flute taps if at all possible. This doesn't mean that I no longer use my extensive range of conventional taps, as I have them covering most families of threads, but new one are spiral flute.

Excellent for blind holes as the Swarf comes out backwards rather than being packed up a blind alley.

Note: There are spiral flute taps, and spiral point taps, and suppliers (particularly on eBay) confuse the two. The spiral point ones are also very good, and considerably more robust than a conventional tap.
Andrew Mawson
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Offline Mike E.

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Re: Tapping -- How to's and How not to's....
« Reply #22 on: May 25, 2017, 05:26:40 AM »
What's the logic in this? Maybe it stays liquid in a really small hole but for any "normal" size it will have evaporated long before having the chance to be helpful. ...............

Have you have tried it ?
Mike

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Offline PekkaNF

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Re: Tapping -- How to's and How not to's....
« Reply #23 on: May 25, 2017, 07:14:07 AM »
DOH. :doh:

Picture of the "sticker" above was from beta print....it has an error.

Finally I have by taps in order and I put 20 boxes on one tool chest tray.

I'm in for spiral taps too. Although one more complication: There is a model that pushes the swarf down! Nice when you do trough holes and front side matters.

Pekka

Offline AdeV

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Re: Tapping -- How to's and How not to's....
« Reply #24 on: May 25, 2017, 10:13:46 AM »

I'm in for spiral taps too. Although one more complication: There is a model that pushes the swarf down! Nice when you do trough holes and front side matters.


Mine do that.... I think that's because they're "spiral point" rather than "spiral flute" (per Andrew's post). They do work exceedingly well, though, and if I have a choice when I buy taps, that's what I buy (no-one does a spiral flute/point left-hand 1/2" UNC* though, for some bizarre reason.)

* I may have the size wrong, going from memory...
Cheers!
Ade.
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Offline sparky961

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Re: Tapping -- How to's and How not to's....
« Reply #25 on: May 25, 2017, 06:56:43 PM »
What's the logic in this? Maybe it stays liquid in a really small hole but for any "normal" size it will have evaporated long before having the chance to be helpful. ...............

Have you have tried it ?

Don't need to.  There are enough chemicals I inhale that are "necessary" to cause me to avoid using them unnecessarily.

Offline Mike E.

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Re: Tapping -- How to's and How not to's....
« Reply #26 on: May 26, 2017, 08:23:08 AM »
Ok, fair enough.

Mike

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Offline ieezitin

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Re: Tapping -- How to's and How not to's....
« Reply #27 on: May 26, 2017, 07:35:47 PM »
Roll form taps.. do a great job the pilot size's are different but are available on the net.... you need a little more power to form your thread but break less if not at all.. most people don't know about roll-form taps which means e-bay sellers sell them cheap.  do your own research they are great.

Anthony. 
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Offline Lew_Merrick_PE

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Re: Tapping -- How to's and How not to's....
« Reply #28 on: May 26, 2017, 10:05:07 PM »
Here's a paper I put together on sizing pilot holes for tapping.

Offline howsitwork?

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Re: Tapping -- How to's and How not to's....
« Reply #29 on: May 29, 2017, 05:48:10 PM »
cheers for the paper to read :thumbup:

I must admit trying roll form taps for aluminium and they work well but I was very concerned about the force I had to use at first. They do seem significantly stronger though.

Count me in for spiral taps, oh the joy of watching the swarf come out ! Cost a bit more but much more satisfying to use especially in the smaller metric sizes. Not got any imperial ones yet.....

I stick to paraffin mixed with neat cutting oil but have also found WD40 works well for ali. Anyone tried milk - seriously one guy I know swears by it! :Doh: