FLAT THREADS

[riversidedan]

Use an F drill . .257

will give that a shot and respond shortly thanx

you were correct the tap went in the 6061 with minimal amount of effort and the bolt fit fairly snug. I see you chose the 257 which is after 250, why would you chose 257?

 

[mmcmdl]

speaking of thread info>>>>>>>>>.I have a 5/16 -18 tap and the chart sez 250 2570 2610 2656 2660
for the hole size to be tapped, am curious which size drill would I use ???

will give that a shot and respond shortly thanx

No need to , I'm off to work !

 

[hman]

I see you chose the 257 which is after 250, why would you chose 257?

The "magic rule of thumb" for tap drills (metric or inch) is to subtract the thread spacing from the nominal diameter. For 5/16-18, the thread spacing is 1/18", or 0.0556. 5/16-0.0556 = 0.3125-0.0556 = 0.25694 ~0.257

 

[rwm]

The "magic rule of thumb" for tap drills (metric or inch) is to subtract the thread spacing from the nominal diameter. For 5/16-18, the thread spacing is 1/18", or 0.0556. 5/16-0.0556 = 0.3125-0.0556 = 0.25694 ~0.257

That's brilliant. First time I have ever heard that. My chart is now in the garbage.
Robert

 

[wildcatter]

the die you are using is a thread repair die. They are a six sided die. The one you should use will be round on the outside.

 

[riversidedan]

have a round Metric set from HF that weirdly enuff work fairly well for what they are and didnt know the ones im posting about were for repair..........anyone else wanna chime in on that>?

 

[savarin]

The "magic rule of thumb" for tap drills (metric or inch) is to subtract the thread spacing from the nominal diameter. For 5/16-18, the thread spacing is 1/18", or 0.0556. 5/16-0.0556 = 0.3125-0.0556 = 0.25694 ~0.257

No wonder I love metric, so much easier.

 

[wildcatter]

do a search on dies for repair or cutting new threads. Im notsaying this is why you have flat threads, just suggesting it may be part of the problem you are having cutting threads.

 

[riversidedan]

I FOUND THIS,

>>>>>>Round dies are usually the choice for cutting new threads whereas hex die nuts are commonly used as a chaser to repair existing threads. Round dies also require a holder/handle to use them, whereas hex die nuts do not. Proper Hand Thread Cutting Techniques Taps Are Brittle – Handle With Care

 

[riversidedan]

No wonder I love metric, so much easier.

curious why you said that?