Self Tapping Screws Don't Self Tap

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

Post Reply
pollys1dad
Posts: 296
Joined: Mon Jun 25, 2012 12:13 pm
Location: Wiltshire United Kingdom

Self Tapping Screws Don't Self Tap

Post by pollys1dad »

Hi,
For woodworking I bought a Trend 50 inch Varijig straight edge clamp guide also a Trend VJS/CG/SQA VJS/CG squaring attachment to fit on the end of it. The squaring attachment comes with two self tapping screws I've tried, quite forcefully but the screws aren't interested in self tapping. The only thing I can think off is use a very narrow drill bit to drill a mm or so down to get them started.I have a floor standing drill press but not any tiny drill bits
I don't want to bodge the fit, as defeats the object of the squaring attachment holding the clamp square on the workpiece.
Attachments
Trend Varijig.JPG
johnfreese
Posts: 219
Joined: Thu Jan 21, 2016 2:10 am

Re: Self Tapping Screws Don't Self Tap

Post by johnfreese »

There are various types of self tappers. Some cut a thread. Some form a thread. Anf then there are sheet metal screws. A photo of the screw would help.
pollys1dad
Posts: 296
Joined: Mon Jun 25, 2012 12:13 pm
Location: Wiltshire United Kingdom

Re: Self Tapping Screws Don't Self Tap

Post by pollys1dad »

Hi Thanks,
I've tried taking several close up photos of the screw. Unfortunately the camera macro feature doesn't seem to work too well.I hope you can make out the type of screw?
Cheers.
Attachments
1.JPG
2.JPG
3.JPG
4.JPG
5.JPG
6.JPG
SLK001
Posts: 8
Joined: Tue Jan 29, 2019 8:53 pm
Location: Coral Springs, FL

Re: Self Tapping Screws Don't Self Tap

Post by SLK001 »

That looks like a self-drilling screw for use in metal (probably other uses too). It won't harm anything if you drill a pilot hole that is less than the diameter of the screw's "drill".

Sometimes these things require a lot of downward force to get them to "start". The fact that it is a pan head and not a hex head makes that difficult.
User avatar
NP317
Posts: 4557
Joined: Tue Jun 24, 2014 2:57 pm
Location: Northern Oregon, USA

Re: Self Tapping Screws Don't Self Tap

Post by NP317 »

I always drill pilot holes just smaller than the minor diameter for such screws.
'Makes a world of difference!
~RN
pollys1dad
Posts: 296
Joined: Mon Jun 25, 2012 12:13 pm
Location: Wiltshire United Kingdom

Re: Self Tapping Screws Don't Self Tap

Post by pollys1dad »

OK thanks people.
User avatar
Harold_V
Posts: 20232
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Self Tapping Screws Don't Self Tap

Post by Harold_V »

The other thing is such screws respond far better to being installed by power than by hand. If the screw head accommodates a Phillips driver, they're pretty easy to install, especially with power. Slotted heads tend to be troublesome unless you have the proper driver, which keeps the blade in the slot. And, as stated, I tend to drill a pilot hole that is barely undersized, thus allowing the screw to determine the desired hole size. Drilling the hole with the screw without a pilot hole can be frustrating.
Wise people talk because they have something to say. Fools talk because they have to say something.
John Hasler
Posts: 1852
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Self Tapping Screws Don't Self Tap

Post by John Hasler »

I sometimes start those screws with a hammer. I wouldn't do so in this case, though. Better to drill a pilot hole. It need not be full depth.
pollys1dad
Posts: 296
Joined: Mon Jun 25, 2012 12:13 pm
Location: Wiltshire United Kingdom

Re: Self Tapping Screws Don't Self Tap

Post by pollys1dad »

OK thanks.
User avatar
Bill_Cook
Posts: 535
Joined: Sat Jan 04, 2003 10:28 pm
Location: Walnut Bottom, PA, USA

Re: Self Tapping Screws Don't Self Tap

Post by Bill_Cook »

Another solution would be to thread the holes with a tap, and use some quality machine screws.
BC

If there was only one way to do each machining job, the smell of sulphurized cutting oil smoke would have fewer fond memories.
Post Reply