Oversize Taps

Google is your friend:

McMaster has them, or wherever you buy your regular taps. Ask your plater how thick the hard anodizing is, and buy the appropriate H number tap. Probably an H3 or H4 will be fine. I personally don't recommend anodizing threads, and wouldn't guarantee them to a customer.

UNIFIED TAPS. The American ¡§H¡¨ System This system provides for a range of pitch diameters for each size of tap: the height limit of pitch diameters being the basic pitch diameter plus increments or units of .0005". It is designated by the letter ¡§H¡¨ followed by a numeral indicating the number or units applying to the particular ¡§H¡¨ size. The tap manufacturer¡¦s tolerance is applied as minus. The ¡§G¡¨ designates a ground thread finish For taps up to and including 1" diameter G H1 ¡V Basic plus .0005" G H2 ¡V Basic plus .001" G H3 ¡V Basic plus .0015" Tolerance G H4 ¡V Basic plus .002" ¡V.0005" G H5 ¡V Basic plus .0025" G H6 ¡V Basic plus .003" For taps over 1" diameter up to and including

2" diameter G H4 ¡V Basic plus .002" G H6 ¡V Basic plus .003" Tolerance G H8 ¡V Basic plus .004" ¡V.001"

Remember, Google is your friend.

As far as how to use them, buy yourself a machinists handbook.

Ask the anodizer how thick his coating is. You can get oversize taps fron MSC An H7 tap is .003 oversize example (10-32 H7) An H11 tap is .005 oversize(10 -32 H11)

this helps

Bad design or call outs. We never anodize threads. Plug the holes, put a rubber on od threads.

Nagesh,

What size tap you run depends upon the plating thickness and what tolerance the plater can hold.

What is the plating thickness call out on the print? What tolerance can the plater hold?

My experience with hard anodize I don't think the plater can hold a tight enough plate tolerance on an #0-80 thru #10-32 tapped hole to where you would not have to rework the tapped holes after hard anodize.

Tom

Nagesh S K wrote:

Nagesh,

If the customer insists on doing it this way, don't guarentee the threads

Anything under a # 10 you want to plug (mask). # 10's only work if they're a through hole. Fluid can't flow past these small features. The liquid gets trapped and becomes exausted without being renewed. The usual result is maybe 1 or 2 anodized threads at the end('s), and a sloppy corodded mess beyond them. Never try to anodize a blind threaded hole under 1/2".

Normal "Type III, Class II" is .0015" to .002" thick, half of it being below the surface, and half above.

HTH

Mark

Nagesh,

Sounds like a mistake on Engineering/Drawing side, someone added a call-out that is not possible to make or in the best of circumstances very difficult. Heli-Coil seems more appropriate for most applications. Suggest you contact your customer and discuss this job, if they won't budge from or revise the print then quote less tap and plate or walk away from it. It will only come back to haunt you , cost you money and possibly a customer. It is better to pass on a job than ship scrap and lose them as a customer.

Tom

Nagesh S K wrote:

Tom and others

Thanks for all your inputs.

I just got the prints. There are two items.

In one of them only two holes needs to be hard anosized. One is #4-40 blinde and the other #10-32 blinde with a dia 1.5mm thru hole at the bottom. All other threaded holes most of them #2-56 needs to be masked.

Other item has about 92 #0-80 holes, 3.5 mm deep and about 35 #2-56,

4mm deep threaded holes all blinde. But this item needs to be silver plated to 0.005mm thick. This drawing calls for over size tap of 0.03mm.

I have contacted North american tools

and requested a quote from them.

Regards

SKN