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tapping threads for jacking bolts
By electrondady1, Section Mechanical Posted on Mon Feb 13, 2006 at 05:12:50 PM MST
must get it right the first time

the little hd mag rotors i made are stronger than i expected. i want to use jacking bolts to lower the top rotor in place and adjust the stator clearance. i bought a set of taps years ago but never used them. i have two candidates one marked,1/2-13 unc the other 3/8-16 unc . i tried to spin a course thread nut on to the taps but they don't really want to go on very far. does that sound right? also , i'd like to know the proper size of the hole i should drill to enshure strong threads. there is a lot of offset in the brake rotors i'm using so in a pinch i could weld a nut in place and use that.

tapping threads for jacking bolts | 11 comments (11 topical)

Re: tapping threads for jacking bolts (3.00 / 0) (#1)
by richhagen on Mon Feb 13, 2006 at 10:29:01 AM MST

My tap set, which isn't at the location that I am at at the moment, lists the drill size to be used with the particular tap. I will check it today and post back the sizes it lists for those particular taps. In general, from my experience only, the tap will spin into a tapped hole relatively freely until the flatter portion of the tap reaches the hole. Then any differences between the original tap used, and the one being used to clean up the threads become aparrent in that you have to cut metal to match, resulting in increased resistance to turning. For the jacking bolt size, I can't see a problem with going bigger, as it would be stronger if the space exists in the rotor, however smaller holes and threads are probably less work if they have sufficient strength for your rotor size, and unless you are building a rotor like DanB's, it probably is, but again that is just my opinion. Rich Hagen
'A Joule saved is a Joule made'

Re: tapping threads for jacking bolts (3.00 / 0) (#2)
by Goose on Mon Feb 13, 2006 at 01:53:54 PM MST

tap drill for 1/2-13 is 27/64 (7/16 will work with plenty of strength), 3/8-16 is .3125(5/16). Either one of them is more than enough strenght to use as a jack for your magnets.

The tap will not go through the nut, probably because the tap that made your nut was getting wore out. Nothing to worry about.
Goose

Re: tapping threads for jacking bolts (3.00 / 0) (#3)
by electrondady1 on Mon Feb 13, 2006 at 02:34:59 PM MST

sweet, that's the info i needed, thanks guys !!

[ Parent ]

Re: tapping threads for jacking bolts (3.00 / 0) (#4)
by RP on Mon Feb 13, 2006 at 09:19:28 PM MST

A few more thoughts:

Use lots of lube when cutting the threads. WD-40 or motor oil is fine.

For threads this size, do them by hand, don't use a drill or some such.

Be careful to keep the tap perpendicular to the surface when starting out. These larger course taps can easily start off on a weird angle.

After it starts to really bite (like 3-4 turns in) back it out a little (frequently) to break the chips off so it doesn't bind up. 1 turn in, half a turn out, 1 turn in out, etc...

On the other hand, welding nuts in should be fine too but I'd weld them on the inside so the stress is not trying to pull the weld apart. That way you could get by with tack welds and less heat, splatter and warpage.

[ Parent ]

Re: tapping threads for jacking bolts (3.00 / 0) (#5)
by electrondady1 on Mon Feb 13, 2006 at 09:30:43 PM MST

well, i'll try to tap the threads first. it seems more classy. if i blow it , out comes the welder, my cure all. just trying to get away from the post apocaliptic road warrior stuff i usually build. thanks rp.

[ Parent ]

Re: tapping threads for jacking bolts (3.00 / 0) (#6)
by richhagen on Tue Feb 14, 2006 at 08:30:57 AM MST

I see that you already have the tap sizes, so no need to reprint them, and like RP says, if you were to weld the nuts, weld them on the inside, that way even if you have freak situation of a bad weld or two, the top rotor won't go crashing down to the other rotor. Rich Hagen
'A Joule saved is a Joule made'
[ Parent ]

Re: tapping threads for jacking bolts (3.00 / 0) (#7)
by rotornuts on Tue Feb 14, 2006 at 06:22:47 PM MST

For future reference, tap drill size can be easily calculated with the following formula:

tap drill size = major diameter - 1/number of threads per inch

TDS = MD - Pitch(1/number of threads per inch)

So for the 1/2-13 UNC it looks like this: 1/2 - 1/13 = 27/64

1/2(.5) - 1/13(.0769) = 27/64(.4231), You find the fractional size by multiplying the decimal answer by fractional denominators 'till you get as close to a whole nnumber for a numerator as you can. 0.4231 x 16 = 6.76 nope. 0.4231 x 32 = 13.5 nope. 0.4231 x 64 = 27.0784 bingo that's as close as we'll come.

Just so you know 1/2 = Major diameter, 13 is the number of threads per inch and UNC stands for UNified Coarse thread.

If you have a tap that says NC instead of UNC it will work for UNC and visa versa. The only difference is in the root and crest of the thread, the basic form is the same.

Mike

Re: tapping threads for jacking bolts (3.00 / 0) (#8)
by windstuffnow on Wed Feb 15, 2006 at 07:46:31 AM MST

Mike, your learning all kinds of things in "school" arent you... Thats some great information, I'll have to remember that...

I have a chart next to my drill press with all the information so I don't have to work my brain ( lazy ).

I did a google search for the chart and one that poped up was ... http://www.engineersedge.com/tap_drill_chart.htm ... just print and hang it up in the shop for a quick reference...

.
Have Fun! Windstuff Ed
[ Parent ]

Re: tapping threads for jacking bolts (3.00 / 0) (#11)
by dinges on Thu Feb 16, 2006 at 12:43:30 AM MST

And for anyone interested in metric sizes (giggle),

Drill diameter is .8x tap diameter. I.e., M5 thread should be drilled at 4.0 mm, M4 at 3.2 mm, etc. (This is for 'coarse' thread, the one that 99.9% of all metric threads is)

It's a rule of thumb, and the actual thread tables are in close agreement (perhaps .1-.2 mm difference maximum). This may be different for your US thread sizes, since these usually use a top-angle of 55degrees, as opposed to metric 60degrees.

Peter.

[ Parent ]

Re: tapping threads for jacking bolts (3.00 / 0) (#9)
by rotornuts on Wed Feb 15, 2006 at 07:15:42 PM MST

That's a nice chart, even has NPT threads. I have a nice little pocket guide that I keep min my coveralls at work. Covers conversions, tap drill sizes and things like drill point depth formulas for various drill point angle and countersinks. Comes in handy for the CNC machines as they don't do fudge very well.

I'm done school for this year but I'm eager to go back for second year. I'm running a Mazak Nexus 510 CNC mill now at a local shop. Lot's of fun! Scary too!

Mike

Re: tapping threads for jacking bolts (3.00 / 0) (#10)
by electrondady1 on Wed Feb 15, 2006 at 09:11:27 PM MST

i printed and pinned mine up. thanks ed . mike, we all expect to see some cool cnc produced vawt profiles out you you soon!!

[ Parent ]

tapping threads for jacking bolts | 11 comments (11 topical)

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