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This information is offered as possible guidelines and/or solutions to problems you may be having and is not intended to discredit or criticize gun drilling procedures currently being used in the industry.) We submit the following as opinions only, based on our experience and judgment.


Q: Why do gun drills whip?

A: There is no way to stop single flute gun drills from whipping, and the faster the RPM the more the tube will whip. The reason is that the tube has been crimped 110-120 degrees. This moves the center of gravity off-center and now the tube is out of balance.

Q: My plastic whip guide bushings get hard after a while, can you tell me why?

A: The chemicals in the oil, sulfur and chlorine, and many other chemicals attack the plastic, and over time the plastic gets very hard. Some people like the bushings harder.

Q: What types of testing have you done on whipping?

A: We built a small device that we could get up to 10,000 RPM. We then took a 1/8 gun drill and had 8 inches between whip guide supports. With standard adaptors, having only one drill bushing installed, we increased RPM until we saw whipping. Around 3,000 RPM the 1/8 diameter tube was whipping about the size of a nickel. We then installed a set of whip guide stabilizers on both guide supports and were able to increase the RPM to 10,000 with very little whip.

Q: What’s so good about the DOUBLE Doodad?

A: The Double Doodad has twice the bearing surface, absorbs more vibration in the chip box caused by whipping, and helps control whipping by shortening the unsupported length. It also creates a better seal in the chip box.

Q: Why do I order Doodads by the tube size and not the drill size?

A: Since tube sizes for gun drills are not standard in the industry, you could order a 0.125 drill from two different manufacturers and end up with a different tube size from each company. It’s also possible to order the same size drill from a company at two different times and end up with different tube sizes depending on which tube sizes the company had in stock when you placed your order. That’s why you might find your whip guide bushings sometimes fit loose on a gun drill size you always work with. If the bushing fits too loose on the tube, it will generate more vibration caused from whipping.

Q: Once in a while when I start a drilling cycle, one of my drill tubes gets bent between the whip guide supports. Is that caused by wind-up?

A: No. It’s not wind-up if the drill tube is bent. This problem occurs when using Stieber Chucks because you’re only supposed to hand-tighten them. What you should do is hand-tighten with a spanner wrench. This should take care of the bending. We have seen a lot of this problem using small drills with high-pressure coolant 1200-1800 PSI. The pressure is hydraulic pressure, which pushes on the driver and moves the driver forward, and bends the tube on the gun drill. When using 3/4 inch Stieber Chucks, you should use plain drivers without the milled section for a set screw and the driver should not measure any smaller than 0.7494.

Q: I have a 20-inch long part with the requirements of a maximum 0.010 runout. Is there any way to control runout?

A: To control runout you must use a stabilizer in the chip box and on the steady rest. The most important thing is to order your gun drills with the tube diameter 0.005-0.007 smaller than the gun drill. If your drill is 0.125, then your tube should be 0.120-0.118, even if this means ordering your tubes center-less ground to get the tube size you need. It’s necessary to have the unsupported length in the chip box as short as possible. This will keep the tube stiff and help control the whipping. The start hole will be straighter and the exit hole will have less runout. If the tube is not stiff and whips, the bending forces are transferred into the drill tip. Because of the back taper on the gun drill, these bending forces will keep the drill from starting straight and the runout will be greater.

Q: Do you make any special whip guide bushings?

A: Yes. No matter what you’re looking for, 2-Flute Whip Guide bushings or 4-Flute Whip Guide bushings, we can get you what you want. When it comes to specials, we can do the mold designs the same day you send in your request. It takes about 4 to 6 weeks to get you the new designed bushing.

Q: When I order my gun drills I am told they don’t have a tube 0.007 smaller than the drill. The only tube size available is 0.015 smaller. Is it okay to use a Gun Drill with a tube 0.015 smaller in size?

A: Yes. It is our opinion that the tube size should never be any smaller than 0.015 than the drill, for up to 1-inch drills, especially if you’re drilling deep holes more than 10 inches deep. If you need to keep your runout to a minimum, you may want to see if you can order your tube center-less ground for the tube size you want before it’s crimped. Try to keep your tube size 0.005 to 0.007 smaller than the drill. We have done a lot of testing on 1/2″ holes. The drills were 0.490 diameter, tube size 0.464 (-0.026). The drills caused us a lot of problems. The drills gave us a lot of vibrating problems. We then tested drills 0.491 with tube sizes 0.484 (-0.007). We ran the same test 2000 RPM with a chip load of 0.001.

We were able to drill 3500 inches with the same drill. Lots of our problems went away and we drilled 3 times as many parts. The material was 4150, PHT to 32 Rockwell. The temperature of our coolant was 100-110 degrees Fahrenheit, using gun drill C oil. On drill sizes of about 0.150, we order the tubes 0.005 smaller than the drill. This has shown in every case to give us less runout. Different materials, different oil, oil pressure, and counter-rotation may give different results. Please share your feedback with us, so we can get your ideas and experience.

Q: Do you make Whip Guide Stabilizers for larger adaptors?

A: Yes. We have designs for the B300 and B400. These are made to order.

Q: What can you tell me about coolant temperature?

A: We’ve gun-drilled with coolant at 100 to110 degrees Fahrenheit and have seen work hardening of heat-sensitive steels such as chrome alloys and tool steels. We believe that such heat-sensitive steels need the heat removed as fast as possible and that a coolant temperature of around 80 degrees Fahrenheit does this better. Work hardening can be a problem for some applications. Faster feed rates will generate more friction, which will generate more heat, and can cause you a lot of problems. If your coolant is not cold enough, the drill can start binding and vibrate due to excessive heat build-up in the workpiece and gun drill tip.

Q: Have you done any testing on reaming?

A: Yes. Many people who ream prefer pull reaming. We have done tests on both. Pull reaming can cause bell mouthing to some degree on both the entrance and exit ends. We prefer push reaming because the reamers never have to come out of the machine. We shut the reamer off at the end of the stroke and pull the reamer back, leaving the oil still on. TIN & TIALN coated reamers will help galling problems. The reamers must be resharpened after the coating has been applied Coolant temperature should be below 85 degrees Fahrenheit to remove heat build-up caused by friction.

Q: What size reaming rod should I order with my reamers?

A: The reaming rods should be hardened to above 45-50 Rockwell C. You should have the rods about 0.007 to 0.010 smaller than the reamer. You should use whip guide stabilizers on your whip guide supports, as well as in the chip box. This will keep whipping from transferring forces into the reamer, thus keeping the reamer straight. Drilled holes should be 0.005 to 0.007 smaller than the finished reamed hole. If you need reaming information, give us a call.

Q: I use Pratt & Whitney gun drill machines. I don’t spin the drills. I spin the part. Can I use the stabilizers, and what will they do for me?

A: The stabilizers will keep the tube from whipping when the drill is spinning at high RPM. On a Pratt & Whitney, the stabilizers will help keep the tube from bending as much. By controlling the bending you will be able to increase your feed rate and drill faster. It is known, that the faster you drill, the higher the coolant pressure should be in order to get the chips out.

Q: What can you tell me about vibration?

A: Vibration is caused by many things. The major vibration is caused by whipping. This type of vibration you will not hear, but you will be able to feel the vibration by touching the part that is being drilled. Another vibration that you will hear, will be when the drill starts to get dull, or a chip welding problem. Another type of vibration that you will also hear is when the chips get stacked up in the drilled part and the drill and tube start to bind up. Chips backing up in the drilled part can be caused by a stuck chip deflector or chips getting too long and wrapping around the tube in the chip box. Another type of vibration you will also hear is when the part gets too hot. This causes the carbide and the workpiece to expand and the drill starts to bind up and sometimes breaks. Another type of vibration you will hear is when the roller bearing in the chip box gets a lot of slop in it. A worn-out roller bearing will confuse you at times and you will change out a drill, thinking that the drill is dull.

Q: I have some DeHoff gun drilling machines. If I use tight whip guide bushings my whip guide supports pull back, and this winds up my gun drills. Do you have a fix for that?

A: If you use whip guide stabilizers with a larger bushing, this will help a lot. The real fix is to reprogram the machine to stop the drill at the end of the cycle. Now the drill is not spinning when the drill returns to home. We leave the coolant on while the drill is returning home. We notified Kay’s Engineering and told them that we reprogrammed our PLC to stop the drill at the end of the drilling cycle. Kay’s can modify your program for you so you can have an option to turn the spindle off at the end of the drilling cycle.

Q: Do you do any testing on your whip guide bushings?

A: Yes: We test them on our own gun-drilling machines. We try to improve vibration control, whipping control, gun drill run-out and also improve drilling speeds so you can maximize your production. So if you have a special application, like two different size holes meeting each other at some specified depth, a flat bottom section meeting another size hole, special reaming or gun boring, give us a call and we will give you any information we have.


Q: Is there any way we can get a better discount based on quantity and take delivery at different times during the year?

A: Yes, we do give bigger discounts based on yearly quantities. We do offer 1-year blanket orders, and we will ship your orders depending on the delivery schedule that is set up at the time we take your order.

Q: How can I tell if I may have overheating caused by drilling?

A: Look at the exit hole. Easily seen discoloration or blue rings means that overheating has been caused by the drilling. If work hardening is an issue, a lower temperature coolant may be needed. In some cases, it doesn’t matter what the hole looks like and drilling time is the only issue.

Q: What is the difference between a Snap Ring vs Doodad?

A: We have tested the snap ring style bushings for over 3 years. They work just fine in most cases, but sometimes the snap ring pliers seem to find feet and walk away. The Doodad was designed with a self-aligning pilot for ease of installation. 16 Doodads can be installed in the bearings in under 1 minute. We use a small No.1 Arbor Press to push the Doodads into and out of the bearings. The No. 1 Arbor Press is less than $75.00 (MSC catalog # 03891207). It’s a great tool to have on your bench to install and remove the Doodads. The No. 1 Arbor Press is also perfect for replacing worn-out bearings in the adaptors.

Q: How can you achieve the perfect diameter in gun drilling?

A: Gun Drills will not give you a perfect diameter hole through the whole part. To get a perfect diameter hole through the whole part (+-0.0002) or better, you must consider reaming the hole if you need to maintain a close tolerance. Using special bore gages we have checked drilled holes using gun drills with a 0.5000 diameter by 35 inches deep to see how perfect the holes were. There were sections that were up to 0.503 to 0.504 diameter using a new drill. We believe the problems to be chip weld causing the drill to move off-center and drilling larger. We also believe that chips could get caught behind the back taper of the drill, moving the drill off-center, causing the same problems. Please share your feedback with us.

Q: What kind of resin is used in your whip guide bushings?

A: Our whip guide bushings are manufactured using only Pure Virgin Resin. We do not buy recycled material to make whip guide bushings. We do not reuse our scrap and mix it with our Virgin Resin. If someone tells you that our material is not the same as theirs, ask them for a data sheet showing you the difference so you can see for yourself.