FLAT THREADS

[hman]

Metric threads are specified by diameter and distance between threads, so it's a simple matter of subtracting one from the other. Inch threads are specified by diameter and pitch. You need to take the inverse of the pitch to get the distance between threads ... an added mathematical step, and one more opportunity for error. Not to mention having to convert fractions to decimals, etc.

 

[Larry$]

M6x1, Tap drill 5mm, 6-1 =5 Now we are talking simple!

 

[riversidedan]

M6x1, Tap drill 5mm, 6-1 =5 Now we are talking simple!

M6x1 die?? tap drill is 5mm??? 6 minus 1 =5 that what you mean???

 

[savarin]

For metric dies the rod dia is the same as its designation, ie, M10x1.25 mm. will cut a thread on a 10mm rod with a pitch of 1.25mm
A M4x0.75 die will cut a thread on a 4mm dia rod with a pitch of 0.75mm

With the taps the same designation is used ie M8x1 mm to cut a 1mm pitch thread for an 8mm bolt
The dia of the hole has to be 8 minus the pitch ie 8-1 to give 7, therefore drill a 7mm dia hole, simples.
None of the faffing about with fractions or obscure decimals

 

[MrWhoopee]

M6x1 die?? tap drill is 5mm??? 6 minus 1 =5 that what you mean???

M6x1 TAP, tap drill is 5mm
M6x1 DIE, stock is 6mm .

 

[riversidedan]

M6x1 TAP, tap drill is 5mm
M6x1 DIE, stock is 6mm .

so your saying the stock is the same size as the part?? such as 6 dia rod uses a 6 mm die? if thats the case the chamfer needs to be pretty steep for the die to get started

 

[MrWhoopee]

so your saying the stock is the same size as the part?? such as 6 dia rod uses a 6 mm die? if thats the case the chamfer needs to be pretty steep for the die to get started

YES!!

 

[riversidedan]

YES!!

 

[SLK001]

so your saying the stock is the same size as the part??

Yes, just as with an SAE (or Imperial) thread.

1/2"-13 thread starts with 1/2" stock.

3/8"-16 thread starts with 3/8" stock.

 

[Larry$]

if thats the case the chamfer needs to be pretty steep for the die to get started

True, sort of. If you take a look in your Machinists Handbook you can find the tolerances allowed for diameter and everything else about threads. The maximum diameter is the full, in this case 6mm, but the diameter can be less according to the MH. Lots of things about threads in that book if you want to get all the information. You can reduce the diameter to make for easier threading, up to a point w/o reducing the strength of the connection. Typical thread engagement is 75%. Even if you go for pointed threads it is normal practice to give a quick swipe or two with a file to knock the points off. (Assumes you are using a lathe.)