Advice on tapping screw threads in metal, please

[cellist]

I'm hoping that someone can give me some tips on how best to start threading a drilled out hole with my taps. Keeping things exactly vertical on all axis' is the problem. I really need a screw sticking out of a brass knob at a right angle, and I don't know if that's just a function of how perpedicular the hole itself is. Any tips?

Also, what lubricant is suggested for brass thread cutting?

Thanks!
Mike

[rodm]

The thread will only be as perpendicular as the hole but you thought that already. First off make sure you have drilled the recommended hole size for the thread you are cutting. Don't think by making the hole slightly smaller you will get a tighter thread - you will only get a snapped off tap stuck in the hole. :mad:

No need to use any lubricant on brass as it chips off very freely. If you feel more confortable with lubricant then a light oil or WD40 will do.
Start with the taper tap as this will go a reasonable distance into the hole and help you align your tap. Start the thread just enogh to feel it bite into the brass (you may have to use some downward prerssure initially) then remove the tap handle leaving the tap sticking out of the hole.

Use a small square and sight your tap on two sides - one at 90 degrees to the first. Straighten if necessary and then put the handle back on the tap.

Stand over your work so you are looking down on the top of the tap and you will find you keep it square. So go ahead and screw the tap in 1/4 to half a turn and then back off (reverse) until you feel it break off the chip. Gently as you go and keep doing this until you feel the tapping free up. This means you have a full length thread cut.

Same again with the intermediate and bottoming taps and you are done. Brass may squeel while you do this but that is a characteristic of brass. Also if the hole is blind be careful when you bottom the tap not to keep turning. Taps are easy to snap in the smaller sizes so it is very much a feel thing.

Suggets you try this in scrap before you attempt your first thread.

[HiString]

I couldn't have said it any better.

One thing I will suggest is to use QUALITY taps and a tap handle that tightens AND stays tight on the tap. I have yet to find one of the cheaper (Asian made) tap sets that come close in quality or performance when compared to a "known" brand.

[Edd]

Put the work in a vice and the tap in a drill press. Slowly move up the table as you turn the tap BY HAND.

[Ashore]

Rodm has given you good advice the only thing I would add is always use a tap wrench never a shifter or spanner , and reomve the tap often and turn job upside down as the material cut away as you tap goes to the bottom of the hole and needs to be removed. If you are using a lubricant you may need to blow these shavings out , using eyewear protection of course
Doing in a drill press will give you a straight tapped hole but increases the risk of snapping the tap as you loose the 'feel' , espically when bottoning with plug tap


Rgds

[garf]

Hi,
If you have enough material to drill into ie depth of the tapping size hole, might I suggest a slight counterbore the exact diameter of the tapped hole. So if you want to drill & tap a 5/16"W hole down say 1/2", then after drilling your tapping size hole, follow up with your counterbore drill 5/16" dia to say 1/8"-3/16"deep. This will help alighn your taps as you cut the thread. This proceedure also gives a neat appearance after you've tapped your hole.
Please beware that brass is easy to drill and tap but don't feed the counterbore drill to quickly into the tapping hole as the drill might "grab"resulting in an overdeep conterbore and too little material to tap.
Regards,
Gary.

[cellist]

Dear Jolly Good Fellows,

Thanks so much for your valuable advice. It's Saturday and the shed awaits. Gonna put on my 'tap' shoes and dance out there to try your wonderful suggestions.

Bestest,
Mike