What size to tap for stripped 10-24 bolts?

[Hilton Ralphs]

Hi folks

I've managed to strip two bolts on my Incra Miter 1000HD. The thread is 10-24 and I'll need to tap a new thread to get the miter gauge to work again. I doubt I'll get an Imperial bolt with a Hex insert head here in South Africa so I was wondering what the next size up would be in Metric?

5mm is a bit bigger than 10-24 but I don't know if the difference is enough once I've drilled.

Am I making sense here?

Thanks.

[Phil Hansen]

JKM in Randburg will be able supply that size. Tapping to 5mm will be a little loose. Best alternative would be to fit an insert (timeset or alternative - also available at JKM). Then there will never be problems with getting obsolete imperial stuff. Phil

[John Coloccia]

You'll have to go to 6mm or 1/4 - 20. I'm having trouble thinking of a bolt hole on the Incra where something like a helicoil would work, but that's nearly always the best solution in aluminum. I'm of the opinion that if it was cost effective to do so, every threaded aluminum hole would have steal threads of some sort from day one, because aluminum, more or less, is lousy at holding threads.

[Matt Meiser]

Aren't all the threads int the incra gauges pretty much into steel or steel t-track inserts?

[John Coloccia]

i'd bet money the holes in the aluminum fence are stripped.

[Bruce Page]

Hilton, the M5 will not have enough thread. You will need to go with the M6 X 1, tap drill size - #9 (.196 decimal) or 1/4-20 UNC, tap drill size - #7 (.201 decimal)

[Hilton Ralphs]

Thanks guys for the feedback. Looks like I'll use either 6mm or 1/4-20 and visit JKM on Monday if Builders don't have something.

Like a plonker I actually managed to strip two of the holes trying to get the gauge to be exactly 90° to the blade. I've tried so many times that not only have I run out of plywood making the 5-cut test but my wife thinks I'm an idiot.

incra_stripped.jpg

Cheers

[John Coloccia]

my wife thinks I'm an idiot.

My wife hasn't seen me screw anything up yet, but doesn't stop her from thinking I'm an idiot...

[Brian W Smith]

As to the effectiveness of a 6x1.00 metric thread.........Don't need to look any further than a Japanese M/C.They can almost build an entire bike using them?Translated;they should be available anywhere...Japanese M/C are.

Metric vs Imperial threads is a deep subject and can almost be an "undiscussable" topic.In anycase,6x1.00 is very popular thread callout.

[Matt Meiser]

Not much thickness in that part so you don't want to go too big and end up with a half a thread in it. I'm thinking 1/4-28 would be better than 1/4-20. If I'm doing my math right, 1.00 is 25.4 threads per inch.

IIRC the rule of thumb is 3 threads in the material minimum.

[Hilton Ralphs]

Not much thickness in that part so you don't want to go too big and end up with a half a thread in it. I'm thinking 1/4-28 would be better than 1/4-20. If I'm doing my math right, 1.00 is 25.4 threads per inch.

IIRC the rule of thumb is 3 threads in the material minimum.

That's exactly what I was worried about. Of course 1/4-28 is not that common any more but I just happen to have bought three such bolts from a local shop (JKM) a little while back as I needed a thumb screw fix for my Stanley #80 scraper which uses such a thread.

I may just try that as I have a tap for that thread as well. I won't be able to use a hex wrench but a normal spanner (wrench) will work.

Ta.

[Bob Wingard]

12-24 is a viable step up if the hole isn't already too big ...there is a 1/4-24 that I'm sure would be a special order ...but it does exist.

[Myk Rian]

According to my Handy Dandy Gorilla thread gauges, 6mm is too close to 1/4". Next size up is 8mm.

[Bruce Page]

According to my Handy Dandy Gorilla thread gauges, 6mm is too close to 1/4". Next size up is 8mm.

He's trying to step up from 10-24.

[Myk Rian]

Duh. Then 6mm or 1/4-20