G Scale Model Train Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
401 Posts
Discussion Starter #1
Does anyone have alot of experience with tapping as I have never done it? Does it involve filling an existing screw hole with a material, letting it harden, and drilling a new sized hole? Any tips, hints, or ideas? Thanks!

-Will
 

·
Registered
Joined
·
188 Posts
I have done a little tapping. The way I have done it was getting a straight bore, either already came that way or you use a drill. Make sure that the bore is narrower than what you want the outcome to be as tapping cuts material. After that it tapping is just like drilling a hole. Always tap by hand and a good precaution is to make a complete 360 degree turn, then back off about 1/4 a turn. By backing off you can prevent the tap from "locking up" which could then possibly break in the hole.
 

·
Registered
Joined
·
214 Posts
If you're re-tapping a threaded hole than you would typically drill a bigger hole and use a bigger tap size than the previous thread size. It's not easy to add material, at least not with metal. Use a drill & tap chart, such as http://www.shender4.com/thread_chart.htm, to find out what size to drill the hole prior to tapping.

You'll need to have a good selection of drill bits to choose from. If you don't already have one, get a 115 jobber drill piece set. Make sure it's HSS (high speed steel) and made in the USA. There's a big difference in price and quality! This is the one I have: http://www.use-enco.com/CGI/INSRIT?PMAKA=300-0027&PMPXNO=2618857&PARTPG=INLMK32

Everyone has different preferences for taps. Personally I like spiral points taps. Again, made sure to get USA-made HSS taps. Quality taps will last a lot longer.



It's pretty easy to do the tapping. Just practice with a soft material (like aluminum or brass). The hardest part is keeping the tap straight. You can buy or make a tapping jig, but I just use a drill press to hold the tap and keep it square with the part. Maybe I should add that it's still a manual process -- I'm not turning the drill press on!

I hope this helps.
 

·
Premium Member
Joined
·
187 Posts
There are charts for drill and tap size charts such as this: http://www.kramerusa.com/DrillTapChart.htm
With steel I go with the recommend size drill but for brass I will go a few drill sizes down. I use a battery drill for taping most of the time. Couple of revolutions in and then out until I get to the depth of the other side.

Use a lubricant for steel and aluminum like motor oil or soap. It's not hard at all. try on a practice piece I think you will be surprised how easy it really is.
 

·
Premium Member
Joined
·
5,510 Posts
I'd recommend getting one of those little black "Pocket Ref" books by Thomas Glover that you find at the checkout of the hardware store (or through MicroMark, etc.). It is filled with all kinds of silly and useless tables and data that can suddenly not be so silly when you realize that it is something that you need. I used to have one at work (I was a computer programmer, but still found neat stuff in it) I also have two in my work shop (one by the mill and one by the lathe) and FOUR of them by my easy chair in the living room (The original one, the wood workers version, the automobile version and a large print version of the original one)!

In this case there are two tables that you need. Page 598 (in the editions I have) is a table of thread sizes (diameter and pitch) and the corresponding size "tap drill" you should use to make the correct size hole to be tapped to the desired thread diameter and pitch. I deliberately dog-eared that page and wrote page number 431 at the top.

Page 431 is the start of a set of tables that give different drill sizes for clearance holes for various thread sizes. I also dog-eared that page and wrote Page 598 at the top for cross reference.

I have no idea why those two tables are so far apart in the book, but they are, so I cross referenced them!

Of course, you may not have the full 130 (or so) set of drills to be able to select the exact one that the table specifies. Also, you may find that harder materials (steel, etc.) may be too hard for you to tap easily. In either of those cases you select the size drill that you do have that is the closest... UNLESS the hole you are tapping is part of something that you are building that MUST be precise in strength... i.e. if you make the initial hole too big there may not be enough material left to form the threads and the bolt may strip the threads under torque or pressure seperating the pieces being bolted together. (Carry this to extreme and assume you have a 1/4 inch bolt and drill a 1/4 inch hole... the threads will slip right through that hole and will never grip!)

If your closest drill size is smaller than the correct one, the tapping will be very difficult and the tap will probaby break, so go slowly, turn 1/2 turn in and back off 1/2 turn, then turn in 3/4 to 1 full turn and back off 1/2 turn again; keep doing the 3/4 in and 1/2 out until you have the hole fully tapped to the desired depth. You may have to remove the tap periodically to clear the chips out (may have to do that even if using the correct size drill!)

Use tapping fluid (oil) on the tap to make it easier. Different materials tap best with different tapping fluids, but any lubrication will help. WD-40 is supposed to be good when tapping (or cutting) aluminium, but I recommend using a general/universal tapping fluid just about everything else. If you are planning to only do a couple of holes in your life, buying a quart of the stuff is maybe not a good idea... so just use 3-in-1 oil or even motor oil.

Be prepared to break a tap or two. They bind, they stick, they break.

Make sure the tap is started in the hole straight. Trying to tap at an angle is like trying to drill a new hole at that angle and the tap WILL break... they are quite brittle and don't bend, they break!

Getting a broken tap out of a hole can be from difficult to totally impossible... depending on the size and the materials. Bigger taps come out easier because you can get down in the flutes with bigger/stronger material to twist it out. Small taps can just disintegrate as you work at them and that usually ruins the hole size. If the tap breaks in brass you can disolve it out with battery acid (or so I am told, I have never tried it...) I usually either dill a new hole to the side or just plain start all over again with a new piece... depends on how much work it is to remake the work piece!

If you have more than one hole to tap in a new piece it is best to attach the work piece to a drill press table (vise, etc.) and drill one hole, then put the tap into the drill press and thread the hole by hand turning the chuck (do not turn the drill press motor on when tapping! Turn the chuck by inserting the key and pulling on it... trying to grip the chuck to back the tap out can sometimes cause the chuck to loosen and let go of the tap). Do at least several threads this way (with that 3/4 turn in, 1/2 turn out sequence) and then do the next hole the same way. If it is difficult to work with the drill chuck this way, only tap the hole for a couple of threads and once all the holes are drilled and the threads started, remove the work piece and finish all the holes by hand using a hand tap wrench. You will have a good start on getting the tap aligned with the hole this way.

Tapping copper is hard to do, it is "grabby". Depending on the particular alloys, brass and bronze can be a dream to tap or that dream can be a nightmare. Aluminium will tap well if you use WD-40 and go slow, although it can suddenly grab and then the acid in the pit of your stomach could dissolve the tap for you! Some steels will tap easily and others won't. Cast Iron, I seem to remember will tap easily once you are past the hard "skin".
 

·
Registered
Joined
·
1,065 Posts
Very nice "tutorials," guys. Yes, they break, I can attest.

I've had success making my own custom bolts and nuts from copper. I make the bolts from 12 or 14 gauge romex grounding wire using a die and then make the bolts from copper plumbing pipe. I flatten the pipe, hammer it flat, drill multiple holes, tap them out and then cut them with tin snips into whatever size bolts I need. I work in 7/8 scale so I can go a bit bigger than the small outdoor scales like 1/32.
 

·
Premium Member
Joined
·
1,696 Posts
Posted By benshell on 02/25/2009 7:08 PM
If you're re-tapping a threaded hole than you would typically drill a bigger hole and use a bigger tap size than the previous thread size. It's not easy to add material, at least not with metal. Use a drill & tap chart, such as http://www.shender4.com/thread_chart.htm, to find out what size to drill the hole prior to tapping.

You'll need to have a good selection of drill bits to choose from. If you don't already have one, get a 115 jobber drill piece set. Make sure it's HSS (high speed steel) and made in the USA. There's a big difference in price and quality! This is the one I have: http://www.use-enco.com/CGI/INSRIT?PMAKA=300-0027&PMPXNO=2618857&PARTPG=INLMK32

Everyone has different preferences for taps. Personally I like spiral points taps. Again, made sure to get USA-made HSS taps. Quality taps will last a lot longer.



It's pretty easy to do the tapping. Just practice with a soft material (like aluminum or brass). The hardest part is keeping the tap straight. You can buy or make a tapping jig, but I just use a drill press to hold the tap and keep it square with the part. Maybe I should add that it's still a manual process -- I'm not turning the drill press on!

I hope this helps.









Ben,

You're halfway there: it's CRUCIAL that the drill table be at a normal angle to the axis of rotation of the chuck. Normal = perpendicular, or at right angles 360 degrees around the chuck's axis of rotation.

Using a drill press for a tap holder is eeehhhh.... okay, but it's far better to use a tap guide, which is nothing more than a circular piece of steel with tap clearance holes in concentric circles.

ANYONE WHO LIKES SUCCESS AND CLEAN, CRISP THREADS SHOULD USE TAP FLUID, KEROSENE, LIGHT OIL (I like/recommend Kroil) TO CUT THREADS. You can pay for 'Tap Magic' but you won't get your money's worth, compared to Kroil.

Les

Retired Tool & Die Maker
 

·
Premium Member
Joined
·
1,696 Posts
Posted By Engineercub on 02/25/2009 6:16 PM
Does anyone have alot of experience with tapping as I have never done it? Does it involve filling an existing screw hole with a material, letting it harden, and drilling a new sized hole? Any tips, hints, or ideas? Thanks!

-Will








Will,

Tapping takes a measure of easily-learned skills and some few aids: 1) Use a lubricant. I like Kroil, an all-purpose penetrant. W/O going into a lot of detail, cutting threads involves heat,though you'd never guess it, and the lube tends to carry that away from the tap's threads, along with the chips, making a cleaner cut and causing your tap to last longer.

Forget chucking into a drill press--or lathe even, unless you know what you're doing and it's necessary. That's an excellen way to frustrate yourself and break taps. Instead, get a tap wrench--I much prefer the T-handle, collet- type to the 'long-armed' kind that are seductively cheap. The reason is, with a fine tap like we use in this hobby, it's ever so easy to get too much side force on the ends of those handles and break a tap. Point of fact, really cool machinists make a set of knurled 'knobs' that fit each tap. (WTH: it pays the same, and gives exquisite control with fine taps).

You must have a tap drill chart: that tells you for X size tap AND thread, you need to drill Y size tap hole, using what's called, oh my gosh, a TAP Drill. Not a special drill, just the drill sized for cutting threads for that particular tap.

DO NOT USE CHEAP TAPS OR DRILLS MADE IN CHINA. Better to go shoot yourself in the foot and be done with it.

For very precise hole location, use a CENTER drill. These come in sets of common sizes, and are very stiff and short. They're used to precisely 'start' a LOCATED hole. Then you switch to the tap drill.

Last, get a TAP GUIDE, which is a circular piece of steel with various tap clearance holes in it: you put the tap in the T wrench, squirt it with Kroil, stick it in the guide hole, feel for that tap hole in your workpiece, and start in.

GO ABOUT 1/4 of a turn. Then back off. Go perhaps another 1/4 of a turn, being sure you 'feel' the tap engage the first try. Regrettably, there's no way to tell you when too much torque is too much. After you break a few taps, you'll know. I broke my share getting up to speed.

ALWAYS proceed about 1/4 turn (or so) and then BACK OFF. This clears the tap threads of chips. You don't have to back all the way out of the hole, but you'll FEEL the chips clear. Eventually, you'll 'clear through', you back your tap out and BLOW (as in compressed air, or failing, a stiff acid brush with Kroil or whatever, you flush out your brand newly threaded hole. Of which you can be justifiably proud.

Brass is 'sticky'. It likes to 'grab' a drill or tap and 'tear' (phonetically: tare) as in rip chunks of metal, rather than cutting clean. Red brass is better than soft yellow brass, bearing brass is pretty okay, the rest you'll learn as you go.

How do I 'learn as I go?" Ever so glad you asked. Your best friend in metalworking is a common 6" mill ******* file, fine cut. You start stroking every piece of metal that comes your way, and you'll learn a repertory of the hardness of metals. Of course you'll get fooled now and then, especially on steel. For those, go to your grinder and hit it with the metal. Watch the color and spray of the sparks. That's all I'm gonna tell you, except after awhile you'll learn 'the feel' of the metal you have in your hands by how fast it cuts--or doesn't--and the color and type of spray of the sparks.

DO NOT GRIND BRASS OR ALUMINUM ON A STONE WHEEL. People who know better will curse and hurt you, and make you clean the wheel. Which I happen to feel is justice. To grind brass or aluminum, use a belt sander.

REMEMBER: Some patience and observation will teach you far better than any ol' guy like me.

Les

Retired Tool & Die Maker
 

·
Registered
Joined
·
1,065 Posts
Les,

Nice tutorial. I ground a large soldered joint on the grinding wheel and the solder impregnated the wheel!
 

·
Premium Member
Joined
·
1,696 Posts
Just use your wheel dresser (you do have one of those, right?
) Clean it off, wiser but not necessarily sadder.

Les
 

·
Registered
Joined
·
1 Posts
As Les said, you can learn much by experimentation and observation. Fifty years hence you"ll have a wealth of knowledge. I'm also a T&DM, and am amazed by how much I've learned in that length of time.

However, assuming that your goals are more timely, here's a couple of tapping tips...

Small taps (I assume that's the current subject) exhibit a very small amount of flexure before they break. The trick is learning to recognize when they flex and STOP.

Support the T-handle in whatever manner is convenient, usually with the left hand. Apply torque to the T-handle bar ONLY with the thumb and middle finger, pointed straight down parallel to the tap. I usually use the first knuckle of the middle finger against the bar on one side, with the thumb wherever it's comfortable on the other side of the bar.

Hold your hand rigid and rotate your wrist. Using this method, your thumb and finger serve as a pressure gauge to monitor the applied torque. The instant the tap stops turning while applying pressure, STOP. Back the tap out a quarter to a half turn to clear the chips and try again. NEVER continue applying torque if the tap stops, lest you learn the manly art of broken-tap extraction. :D

Start by tapping some holes in thin aluminum (1/8" or so). You'll get a feel for what's going on pretty quickly.

Be sure the drilled hole and the tap are both square with the work surface (unless you're doing an angled hole). It's essential that the tap be accurately aligned with the axis of the drilled hole. Mis-alignment is one of the main reasons for tap breakage.

The size of the pilot hole is important. Buy a set of name-brand US-made (or OSG/Sossner (Japan) or Guhring (Germany) drill bits in number sizes 1 through 60. In this series, smaller numbers indicate larger diameters. The series actually goes down to number 90, but 61 through 90 are quite small and seldom used.

If you're tapping hard material (steel, stainless steel, bronze, titanium), you want to use a larger drill bit than is shown in the table of drill sizes. This will result in slightly less thread, but it's much easier to tap the larger hole.

- Leigh
 

·
Premium Member
Joined
·
6,042 Posts
Great tutorials gents, any hints for the dies? I sometimes need to make specialty bolts and screws.
John
 

·
Premium Member
Joined
·
1,696 Posts
Compared to taps, dies are pretty straightforward. Best to use is a lathe, trust me. Lacking that, dies will get the job done. Just use some sort of cutting fluid. Tap Magic is popular, I've used it and don't like it, Kroil is cheaper and smells far better. (I use it for aftershave.)
WD40 is okay ... I guess. ANYTHING is better than nothing, in the way of lube. Even a bar of soap. (Seriously.)

You have to measure your stock diameter, do a look-up in a machinist's handbook or tap/DIE chart, or you run the risk of shoving a die onto an oversized piece of stock. Called 'crowding' by some.

It's harder to get a die started 'normal' to the axis of the stock to be threaded, due partly to the long handles of the die stock, but a little practice and a deft feel will put you to rights. 'Normal' is defined as a true right angle to the axis of the stock to be threaded. Many folk just shove a die onto the workpiece and start twisting, depending upon the die to center itself. Then wonder why threads are sloppy.

Hope this helps.

Les
 
1 - 14 of 14 Posts
Top