Posted by: paul Yacoob ® 02/17/2006, 17:42:11 Author Profile eMail author Edit

What would be the best Dia. for a pilot hole to drive a Roll Thread 2-56 flat head in to. Screw should withstand an undoing Torque of 4 - 4.5 Lb/in, Material is Cast Aluminum 0.077"/0.076" Dia. was tried, The screw is breaking loose at 3.0 Lb/In.

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Re: Roll Tap
Re: Roll Tap -- paul Yacoob	Post Reply	Top of thread	Forum

Posted by: randykimball ® 02/17/2006, 18:06:48 Author Profile eMail author Edit

Is it stripping or breaking loose? If it is stripping you may have a coolant problem. Bye the way, try pitch diameter for the hole size... (see last comment). If it is breaking loose you may need to use a thread locking compound. Also, it could be the screw's fault. Pick a screw and GH size of thread tap that give you a proper combination fit. I'm thinking your screws are loose in the holes..... am I right? So, if so, you could back down one or two on the tap GH size. The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Fri, Feb 17, 2006, 18:08:26

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Re: Roll Tap
Re: Re: Roll Tap -- randykimball	Post Reply	Top of thread	Forum

Posted by: paul Yacoob ® 02/17/2006, 18:49:11 Author Profile eMail author Edit

Thanks for replying to me, I am using Rool Taping screws and driving them in to already casted pilot holes, so the screw itself is forming the threads in to the casting. I supose the altimate quastion remains to be: WHAT WOULD BE THE MINIMUM DIAMETER OF THE PILOT HOLE? in order to give a good enough tightness so the screw would not breake loose easily

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Re: Roll Tap
Re: Re: Roll Tap -- paul Yacoob	Post Reply	Top of thread	Forum

Posted by: randykimball ® 02/17/2006, 23:32:17 Author Profile eMail author Edit

Are you over tightening the threads? If you over tighten the self taping screws you will damage the threads. Cast aluminum will not stand over tightening of the threads as the material forming the threads will break off. As for hole size, measure the shank of the screw between the threads and make your hole a couple of thousands of an inch larger. Also, can you use a longer screw with a deeper hole? This would gain you more holding power. If the material with a tight hole will not hold the torque you require you will have to do one of four things. 1. Increase the screw size 2. Make the hole deeper with a longer screw (more engagenent) 3. Change the material you are threading in to 4. Bond the screw into the hole The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Fri, Feb 17, 2006, 23:44:06

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