Spiralok - female internal thread

How is a thread tapped from the bottom?

No, drill and tap the hole normally then use the Spiralok as per manufacturer specifications.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

Ken,
WADR, did you Google Spiralock? Spiralok is a typo, by the way. The Spiralock threadform is non-symmetric, uni-directional, or whatever you want to call it. That is, it is meant to hold in one direction. Granted, the OP isn't real clear. However, I think it sounds like he's needing to tap holes with a Spiralock threadform tap. If they are through holes, the tap must be started from the correct side.

Tom,

I think anyone who understands the Spiralock concept would understand why the holes have to be tapped from a certain side. You shouldn't try to have anyone fabricate your parts unless they understand this. Otherwise they'll just tap from whatever side they want to no matter what the drawing says.

No, he's talking about using a Spiralok female thread form (usually designated with the suffix -SPL). It takes a special tap that produces a non-symmetrical thread, so it must be tapped from the proper side so that the "wedge ramp" is oriented in the proper direction.

As far as I know this type of hole is always tapped from the screw-entry side, since this is the only side that blind holes can be tapped from, and they only appear to sell one type of tap. For a through hole it would be necessary to indicate which side to tap from.

I would simply call out the hole with a leader line and arrow stemming from the side to be tapped from (preferably in a side view) and add "TAP FROM THIS SIDE" to your thread note. But calling out the hole to be tapped on the "OTHER SIDE" should also be clear, since that is also a common marking for counterbores, etc.

Don
Kansas City

Just to eliminate the confusion, and the presumably dire results that would ensue if you specify Spiralock threads and get 'em cut backwards, I'd go out of my way to not allow through tapped threads. Make 'em all blind.





Mike Halloran
Pembroke Pines, FL, USA

I guess that would work as long as the material thickness is more than about twice your nominal diameter. Otherwise...not a good plan.

Don
Kansas City

Thanks guys,

sorry for my delay, iv been off sick!

Don your response seems the most understanding and accurate! What i cant seem to find if there is a standard way show which way the holes should be tapped from. In guess that it is just a simple note on the drawing coming off of each hole!

Cheers for all your help guys.

p.s. we have to have through holes im afraid.

I'd put a note with leader/arrow indicating "tap all holes from this side" (if that's the case) in at least 2 views, plus maybe pull out a magnified section thru a hole showing the approximate thread profile and repeating the note.

"Tap from opposite side" is an acceptable note, but usually my second choice, just because.

It sounds like you have multiple holes of differing sizes that are variously tapped from either side.

Have you considered a hole schedule? Then you could call one side "A" and the other side "B" and put a column in your schedule that denotes which side to tap from for each hole, in addition to the thread-size and center coördinates.

Don
Kansas City