Gallery, Projects and General > How to's
Tapping -- How to's and How not to's....
Lew_Merrick_PE:
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 lubricant! Tap-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.
AdeV:
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.
raynerd:
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!
Stilldrillin:
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
Bluechip:
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
Navigation
[0] Message Index
[#] Next page
Go to full version