I routinely have to tap 6-32 holes in the sides of 6061 aluminum 1/4 round by the hundreds. I thought I had it wired for a while, because I was able to go through about 500 pieces before breaking a tap. Not the end of the world. But today I broke 4 to go through the same amount. I'm doing it the same way I did in the past, but something is going wrong.
At any rate, I feel it's the lateral movement that is hurting me. On the ones where I'm able to get the tap to go in perfectly straight, you can feel that there's less resistance. The problem is that because it's a round, it is very hard to get the piece clamped so the hole is perfectly straight. I've been using a power drill, mainly because it allows me to kind of adjust the angle a little if I feel too much resistance. I would prefer to use a drill press with tap head, but I don't know how you would align the hole with the tap properly, since the part is round.
I'm not sure how they would do this in automated tooling. I guess maybe do both the hole and tap at the same time somehow. I can't put each piece in a clamp and move it each time, because that would take forever. So I'm kind of at a loss right now. Breaking $40 of taps a day isn't an option. Not to mention the time spent remaking the parts, as the tap almost always breaks off without anything left sticking out to extract it.
I usually hold round stock to be cross tapped in the vise, but with just a bit of clearance so the part can float and align. Using parallels held apart with springs or bent spring flat stock, the round stock will pretty much self center. It's easy to find center between the jaws with an edge finder. Personally, I don't have any trouble lining up the hole to the tap close enough that it won't self align as the tap enters.
I have a simple part I make for one customer that is 1/4" SS rod into which I drill and tap 4-40 cross holes. I have two fixtures with a deep groove centered lengthwise, and expanding clamps that force the rods against the sides of the groove. I spot drill both sides of each rod (have through holes in the fixture) so I don't have to deburr the holes manually, drill, then bring to the drill press where I tap them. This insures they are aligned properly for tapping. These rods are then sawn between each tapped hole and the ends deburred. Sounds a bit like your parts.
Another option if you have holes with regular spacing, would be to machine a half round groove for the material. Drill a through hole to clear the tap, and insert a pin centered along the groove at the hole to hole distance. Pin need not pass through the part, setting into the bottom of the groove will insure alignment so long as the pin is close to hole dia at the bottom.
I've tapped a few hundred holes with a power drill. Haven't broken many taps, but then I'm almost always tapping a hole perpendicular to a flat surface, making it easier to reference if the tap is square.
As bob pointed out, get a "tap and drill" combination - several companies make them - one shot gives you a tapped hole - and for aluminum you can use a tap that forms the threads rather than cuts them - that way you get stronger threads and a stronger tap and less swarf and much less change of a swarf ball jamming up the tap
I've a similar job. I've mounted the motor/chuck from an old battery drill adjacent a linear drawer slide with an angle bracket on it. I've wired a reverse switch to the motor. I hold the work against the angle plate and slide it on/off the tap controlling motor dirction with the other hand. I can knock out M3 threads thru 2.5mm aluminium in about 10 seconds each. Oddly enough I've been using methylated spirits for cutting fluid (flammable I know). It seems to work ok and clean up is easy.
How about a drilling/tapping block with a hole for the rod and a cross hole for the drill and tap? If you are doing it by hand making the cross hole large enough for the tap would likely align the drill close enough. Or you could use two holes and slide the rod accordingly.
These are all good ideas guys, thanks. I think there's multiple options. I think the idea of not holding the part in a 100% fixed position is good. I actually think that's the biggest problem. I think if I did fix it so the part is held, but still allows to adjust itself, that could help. Maybe if I had the tap head I could almost just hand hold it in a V block and kind of guide it, while allowing the tap itself to kind of adjust it slightly as it goes in.
If I just tried using the forming type of tap in the hand power drill, do you think I'd break less by doing that than the normal gun taps?
I would ultimately love to use the combination drill/tap. That would be a huge time saver. But that would at the least need the reversing tap head. The Tapmatic ones are more money than my whole press is worth. Has anybody ever had success with any that are a little less?
Also... On the combo ones, it would seem like there would be a lot of room to screw up. The drill portion and tap portion are obviously working at two different speeds, so even if you were doing it with a reverse tapping head, I would assume that theoretically you could start the tapping portion in before the drilling portion is finished. I'd think that using something like that would work best with something automated, where you could control things more exactly.
I use combined drill-taps for volume tapping. They go for about $8 each. When things are going right, I can do many hundreds of holes with one tap.
It may be hard to do if you are trying to start on a curves side, though. Usually, you would do this in at LEAST a drill press, and possibly spot with a spotting drill or lathe center drill first, then use the tap. In a really rigid setup, though, you could probably start the drill very slowly, and then increase the feed after it has a good start.
I had been using a Procunier tapping head that reverses when you start to retract the tap. I have now got my CNC'd mini-mill set up with a spindle encoder and a servo drive on the spindle motor, so it can reverse to back the tap out of the hole. It centers, drills and taps the hole in about 10 seconds.
By doing the center, drill and tap all in one operation, there is no question that it is straight. I'm doing this mostly with 4-40 holes. I really think even 6-32 is way too fragile for hand feed with a drill. It is too heavy and the torque throws off your feel of the forces on the tap. Still, you might try spiral-flute (NOT spiral point!) taps to see if they are more supple.
Sounds like you are not into CNC there, but you CAN get a Tap-Matic tapping head for a drill press. With the combined tap-drill, you'd do both operations with hand feed in the same fixturing of the part, so it would be straight. You need a depth stop on the drill press so the tap can't goo too deep. A wobbly drill press won't do on this round part, it needs to have a rigid quill to start the hole dead center. A bench-top mill-drill should handle it, though. Jon
I bought an $800 Procunier CNC tapping head for about $100 on eBay. I suspect the TapMatics are going for even less.
If you are doing HUNDREDS of these parts, then such tools start to make a LOT of sense! If you haven't seen these tap drills work, you'll CRY when you first see one do it's stuff!
Yes, it does, no question about it. But, the distance between the drill and thread is built into the tool. I assume you can get them with different lengths of drill, to make sure the drill is all the way through before picking up the feed for the tapping.
Well ... aside from the fact that you're using 6-32, the weakest thread and the most likely to break in the inch thread sizes ...
Did you change the brand of tap?
The style of tap? (e.g. replaced two flute spiral point gun taps with standard plug taps?) A starting tap could get you started a bit better, but you might have to change to plug taps to get proper depth threads all the way through the workpiece.
The size of tap drill? The alloy of aluminum?
The coolant which you are using with the tap? (For coolant in aluminum, spritz the tap and hole with WD-40. It is almost kerosene, which works fine for the purpose too.
Hmm ... with a tapping head, you might be able to use combination drill and taps for this job. The drill part would break through before the tap start started working I would think.
O.K.
====================================================================== MSC part # 00574186 Price: $14.48 ea
Description: HSS Combination Drill-Taps Thread Size: 6-32 Size: 0.1115 In. Material: HSS Thread Size: 6-32 Number of Flutes: 2 Ground Thread Limit: H3 Size (Decimal Inch): 0.1115 Length (Inch): 5/16 Thread Length (Inch): 15/32 Material: HSS Overall Length (Inch): 2 Big Book Page #: 215 ======================================================================
O.K. It looks as though the drill part is 5/16" long, so it would break through before the tapping starts. The tap section is
15/32" long -- enough to do a proper thread through the 1/4" diameter round stock.
Use a tapping head of the kind which has a torque limit. Start with the limit set to the minimum. Drill through with cutting fluid. The start the tap. The clutch should start to slip. Slowly increase it until you can complete the hole, and then adjust the clutch just a bit more torque. Then, when to clutch starts to slip again, it is a sign that the tap has gotten too dull to continue to use, and you should replace it -- *don't* increase the torque setting, or you will break more taps.
Since your hole will be drilled by the same tool as the thread tapping is done, they *will* be in line. Anything which requires changing tools will lead to misalignment.
Set up some kind of jig to guide a center punch between the jaws of the vise so you will have a center punch truly on the top so the drill won't try to skitter sideways around the curve of the round stock.
The expensive part will be the tapping head -- especially if you need to buy it new. (I got mine over time from eBay sales and similar.)
Here is the one which looks right for your task:
====================================================================== MSC #: 00447391 Price: $661.97 ea
The photo shows that it has the torque limit collar at the top, and the 30X is the right size for the smaller taps -- #0 up to 1/4"
If you look through their catalog, you will find various mounts. This one is 3/8-24, which means that you will need an arbor to screw into it -- either one which will be held in the chuck, or better one which converts it to the Morse taper for your drill press. The heads are made with Jacobs taper sockets so you can use standard drill chuck arbors. I took a No. 2 Morse Taper blank and turned the end to fit the threaded socket in my head -- a larger diameter thread, IIRC.
That's what I've described above.
An alternative involves a CNC mill which would drill then automatically change to a thread forming tap and do a thread forming pass on the workpiece, which would make better threads in soft aluminum, but which would be a problem when you have to change between drill and tap unless you have a turret head on the drill press, like a Burgmaster (which is what my first tapping head was made and marked for.)
There are also good broken tap extractors. Check Waldrom, and you need to have the right version for the number of flutes your tap has. A gun (spiral point) tap will have two flutes in that size, and will be a lot better for the task than a 3-fluted hand tap. The spiral point chases the chips ahead of the tap so you don't have to constantly reverse the tap to break chips. The combination tap and drill has a spiral flute tap which tends to move the chips up above the workpiece.
But can you use the combination drill and tap with thread forming taps? Thread forming taps need to have the holes somewhat lager to allow the stock displaced by the tap to form threads near the center of the hole, and when you try to back the tap out, you will wind up trying to cut away that displaced stock -- with the drill bit running backwards.
I think that with thread forming, you are stuck with a separate drill and tap.
A thread forming tap has less lead-in taper than a gun tap, so it requires a more automated system than you can handle manually -- unless you have quick-change collets to swap drill and tap in the same head.
Have you looked at eBay? I find four of the 30X ones there at the moment, and only one is even up to serious money as I type:
Auctions:
310108611663 $117.50 (1 Hour 45 minutes) With MT-2 shank and adaptor for R-8 mill spindle. 16 bids
110325747423 $10.50 (3 hours 20 mins) (five of them, but you need to get your arbor for your drill.) 2 bids
150315664537 $51.00 (3 days 21 hours) 1/2" straight shank to go into your drill chuck. 4 bids
130276363480 $9.99 (6 days 1 hour) 1/2-20 thread mount to arbor. no bids yet.
There are also four more in the "Store" section of the list, ranging from $150.00 to $505.00
The last of those looks like the best bet (other than the lack of an arbor), because it has all of the wrenches needed. The wrenches need to be thinner than the typical open-end wrench. I just got through using a surface grinder to grind down one open end wrench to fit part of mine, and I still need to do so on another wrench (5/8" IIRC) to handle the larger fitting on the collet closer nose. The Allen key is to adjust the clamping plates for the square end of the tap's shank. The Rubberflex collet resists pull-out of the tap.
You'll still have to buy the right size RubberFlex collet (the smaller of the two listed in MSC for the tapping head) for your 6-32 taps. I had to by new Rubberflex collets for each of my Tapmatic heads, as there was only one in the whole combination, and it had the rubber attacked by a cleaning solvent or heat and turning to goo. :-)
Why? The drill speed calculated is for maximum production and wears out the drill sooner than a slower speed. Select a speed for the tapping part, and just be a little more patient in the drilling. You'll save so much time in not having to change drill and tap all the time that you will be ahead of the game to start with.
If the workpiece it too thick. The one which I found for 6-32 in MSC has the drill part 5/16" long, so the point will exit before the tap starts its work. If you were using something thicker, you would have problems, because the tip really *must* clear the workpiece before the tap starts to work. Otherwise, it tries to feed the drill too fast.
BTW -- if you set things up right, you could probably hold a square collet block in a drill press vise, and just slide the workpiece into a
1/4" 5C collet. They collet block sets have both square and hex, and have either a screw in or a lever closing collet closer. Go for the lever one for this -- and if you need the cross holes a specific distance from the end, add a collet stop inside the collet to make things repeatable.
This applies more to the thread forming tap than to the TapMatic, I think.
BTW I've no connection to any of the auctions which I listed. They were simply what an eBay search for:
Tapmatic 30X
turned up. If I did not already have that size, I would probably be bidding on one myself. The prices have gotten nicer over the years. :-)
If this is something that you have been doing with success in the past, and now without anything else in your methods changing you are having trouble, then look first to the aluminum material being a different grade or quality, and second to the taps as being either a poor grade or somewhat odd-size as in plus .003" or something like that.
Take care.
Brian Laws>I routinely have to tap 6-32 holes in the sides of 6061 aluminum 1/4
On Tue, 16 Dec 2008 19:48:33 -0800 (PST) in rec.crafts.metalworking, snipped-for-privacy@earthlink.net wrote,
In my experience, that's a bad idea. It's most important to start the tap as straight as possible. As soon as the tap cuts the first crooked thread, it will try to use that to guide itself the rest of the way. Not the hole. #1 cause of broken taps in hand tapping.
You don't say what's attached to the rod, but if you're going to end up putting screws into the holes, see if you can't just use self-tapping screws.
I can't imagine how you're able to drill or tap that many holes anywhere near where they need to be with a handheld drill motor. I wouldn't even attempt 50 holes in round stock, let alone 500 without a drill press and some sort of improvised fixture. And a good cutting lube. And good lighting.
A cheap Chinese drill press costs about $50, but may not last long, but a better drill press would run for quite a while, but that's a lot of stopping and restarting.
Cheap AC motor machines don't reverse to remove the tap, so a balanced handwheel on top of the spindle pulley would allow the operator to back the tap out (6 turns, maybe).
A better solution would be a cheap drill press, but replacing the AC motor with a DC motor which would be reversible, and could handle the repeated stopping and starting much better. There wouldn't be much coasting to deal with, but an electric brake (normally on when motor is stopped) would almost eliminate any coasting of the motor armature and spindle motion.
If the drill was properly guided to hit the centerline, a cheap quick change hex bit chuck (the kind available for swapping bits in drill motors) would be adequate for that size drill and tap. They would both be too small to just grind a 1/4" hex on their shanks, but a little lathe work with some
1/4" hex brass would turn out some hex adapters very quickly.
Instead of swapping the drill and tap repeatedly, the combo drill-tap tool would most likely last a long time if guided, supported and aligned properly, rather than being run with a handheld drill motor.
Those are some impressive quantities that you were able to do by hand, though.
You don't say what's attached to the rod, but if you're going to end up putting screws into the holes, see if you can't just use self-tapping screws.
I can't imagine how you're able to drill or tap that many holes anywhere near where they need to be with a handheld drill motor. I wouldn't even attempt 50 holes in round stock, let alone 500 without a drill press and some sort of improvised fixture. And a good cutting lube. And good lighting.
A cheap Chinese drill press costs about $50, but may not last long, but a better drill press would run for quite a while, but that's a lot of stopping and restarting.
Cheap AC motor machines don't reverse to remove the tap, so a balanced handwheel on top of the spindle pulley would allow the operator to back the tap out (6 turns, maybe).
A better solution would be a cheap drill press, but replacing the AC motor with a DC motor which would be reversible, and could handle the repeated stopping and starting much better. There wouldn't be much coasting to deal with, but an electric brake (normally on when motor is stopped) would almost eliminate any coasting of the motor armature and spindle motion.
If the drill was properly guided to hit the centerline, a cheap quick change hex bit chuck (the kind available for swapping bits in drill motors) would be adequate for that size drill and tap. They would both be too small to just grind a 1/4" hex on their shanks, but a little lathe work with some
1/4" hex brass would turn out some hex adapters very quickly.
Instead of swapping the drill and tap repeatedly, the combo drill-tap tool would most likely last a long time if guided, supported and aligned properly, rather than being run with a handheld drill motor.
Those are some impressive quantities that you were able to do by hand, though.
I haven't tried anything like this, but maybe you could custom grind a tap to create a pilot, the way counterbore cutters are formed.
I would think it could possibly just be a waste of a tap, but grinding an accurate pilot on the end of a forming tap may actually help get the tap closely aligned with the hole. I have a drill from a fleamarket junk box that has a pilot brazed to the drill point, and it works better than I thought it would. I would guess that about the only way to accomplish a pilot on a tap would be with a precision tool and cutter grinder, forming a tapered lead-in that duplicates the original start for the forming portion of the tap.
What Brian and some others suggested, the alloy may be different (maybe the most likely change), and/or the tap size designation Hx, or the hole size may be different due to feed/speed changes etc, or possibly even the drill size may be slightly different.
Thanks for all the help everybody, I appreciate the effort. The holes themselves are drilled on a press. I do that with a jig I built that has quick release clamps that just locks the round in. I can't use the press to do the tapping because I don't have the reverse head. But if I did, I would just go with the combo drill/tap, because it would be silly not to, and it would be too hard to re-align the hole for the tap once you take it out of the clamp. I've been doing the counter sink by just pressing each one against a counter sink for a few secs.
But yes, believe it or not, up until now I had been doing 500 or more on one tap by just putting the piece in a vise and using a power drill. I put a dab of lube in the hole and it seemed to work fine. I was using the same aluminum from the same dealer, same alloy as far as I can tell, and the taps look to be exactly the same as the past ones. So I don't know what started going wrong.
But I will probably get the tap head and that will save a lot of time in the end. I notice HF has one, but it doesn't appear to have the safety clutch.
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