designing my own gundrill

[Mordecai]

I maybe missed your projected diameter. As long as you can grind a good point I YHINK you could be ok. You might look into using stress proof steel tube or round rod it may not warp as much if you cut a groove for the flute. Otherwise you might try 413 or 4240 round stock. Try aircraft spruce or mc master Carr for material . There may be an exact size you need. Turning a long skinny rod is a challenge for sure. Mak sure your late tracks dead straight. . You can get turned, ground and polished material. Maybe try discount steel . They are based here in minnesota but I think they have a branch in Texas. Mark williams is a big supplier for the drag race guys he also has extensive machine shop services at reasonable rates. He may do center less grinding too . A big part of your project will be grinding an accurate cutting edges. Another thought is carbon fiber rod or tubing CF is far stiffer than any steel there are lots of epoxies that will stick anything to CF. Maybe consider slipping CF tube over the steel to stiffen it . It’s not an easy material to machine carbide woks but CF is abrasive . It’s tensil strength is over 5 time that of steel so you don’t need super heave wall but solid rod would be very stiff . I YHINK CST composites is still around. They have all sorts of Kevlar and CF plus epoxies. We use quite a bit of CF in our rc airplanes. I’ll be interested in your progress and thoughts. What ever you do with CF be sure all safety stuff is in place. You don’t want CF dust or particle on you or in you. I can’t imagine getting a sliver in an eye. Iweare safety glasses all day even eating. They are bifocal but the only eye ware
Byron
are that helps me at all .

hadn't considered on building the CF rod. you are an angel. would it need to cure in an autoclave? say no, please! To unite in the bit? What glue would you use? Loctite?

 

[SmithDoor]

What are you trying to drill ?

I have drill oil holes in stainless over 12" I think 16" on a engine lathe. It is a pain and takes a long time.

Dave

Hello my friends, i got some drawings of gundrills and d bits and i'm thinking about soldering a shank to cooling the bit and expel the chips. Then questions popped into my mind: could you use a steel capillary tube? if the answer to the above question was yes, what diameter of the hole would be enough to have a good flow of fluid? the bit I'm designing has only 2.5mm of space where the hole can be drilled (it's the traditional D-bit in which the cutting area is milled to half the diameter, that is, 5mm -2.5mm= 2.5mm. a hole 1mm into that 2.5mm area of this D-bit, would that leave 1.5mm and exactly 0.75mm of wall. Would that 0.75mm of wall thickness withstand the pressure of 1000psi? would the 1mm hole provide enough fluid flow for the troughs to come out? still on the stem: the rod with a smaller dimension than the bit, but without a flute, would it be possible for the chips to come out around it?

 

[Vietti]

Did anyone ever reply to the question if a D bit needs or can profit from a drilled pilot hole??

 

[Mordecai]

What are you trying to drill ?

I have drill oil holes in stainless over 12" I think 16" on a engine lathe. It is a pain and takes a long time.

Dave

I'm trying to drill stainless steel too! But it's deviating 1mm in 16". I wanted to improve the result and I heard that D-bit does the trick.

 

[Bentwings]

hadn't considered on building the CF rod. you are an angel. would it need to cure in an autoclave? say no, please! To unite in the bit? What glue would you use? Loctite?

We done cure it in our models. I think if you brazed the carbide to the steel rod then used a CF tube epoxied to the rod it might be stiff enough. Not sure how you can clear chips. I could see a small tube for blowing air or coolant with a largCF jacket covering both put enough roost so it it fills the gaps internally it’s getting complicated.
Byron

 

[Bentwings]

We done cure it in our models. I think if you brazed the carbide to the steel rod then used a CF tube epoxied to the rod it might be stiff enough. Not sure how you can clear chips. I could see a small tube for blowing air or coolant with a largCF jacket covering both put enough roost so it it fills the gaps internally it’s getting complicated.
Byron

We use zap epoxies from the hobby shop.
I YHINK you can get them from Robert landing gear. I don’t have their link St Charles no. Is their state. Horizon hobby, tower hobby our local hobby shop. Sky hobby , Eagan minn. he is very good about shipping very friendly . There are a number of other epoxies too we usually say try it first before going all out. I’d make a simple test
Byron drill , not long just get the mfg process down before going all out. Maybe braze a carbide tip on steel rod and drill a hole then add CFand try again
Byron

 

[SmithDoor]

I'm trying to drill stainless steel too! But it's deviating 1mm in 16". I wanted to improve the result and I heard that D-bit does the trick.

The smaller hole the harder is to drill.
If can use larger drill.
The auto industry has specialized drill press for drilling deep holes.
I could take a day of drill a hole.

Dave

 

[Spitfire builder]

Hello my friends, i got some drawings of gundrills and d bits and i'm thinking about soldering a shank to cooling the bit and expel the chips. Then questions popped into my mind: could you use a steel capillary tube? if the answer to the above question was yes, what diameter of the hole would be enough to have a good flow of fluid? the bit I'm designing has only 2.5mm of space where the hole can be drilled (it's the traditional D-bit in which the cutting area is milled to half the diameter, that is, 5mm -2.5mm= 2.5mm. a hole 1mm into that 2.5mm area of this D-bit, would that leave 1.5mm and exactly 0.75mm of wall. Would that 0.75mm of wall thickness withstand the pressure of 1000psi? would the 1mm hole provide enough fluid flow for the troughs to come out? still on the stem: the rod with a smaller dimension than the bit, but without a flute, would it be possible for the chips to come out around it?

Have a talk to Pacific Tool & Guage , they supply deep hole drill bits ,reamers,rifling buttons in carbide

 

[DavidBC]

Hi David, that gundrill project you shared on the Forum was in another thread of mine. I disturb, I'm like that. Forgive me. By the way, I know very well whose project it is. From Howe. From the book "Modern Gunsmith, Howe". I have it, both volumes. I read every day. I have a ton of prints, posts and cad drawings from gundrill and reamers. But there are things he doesn't address, maybe because it's so simple. What made me look for the D bit was the fact that I couldn't get the rod and thought about how I could manufacture it. But I theorized a concept. I even shared it with another friend. I hope he doesn't think I'm an *****. Hahahaha. thanks for your time. And forgive me for perhaps using jargon that is not present in your language. I don't speak English fluently.

You are correct I also have the 2 books and also the 2 in PDF format.

 

[DavidBC]

You are correct I also have the 2 books and also the 2 in PDF format.

They use aircraft frame grade tube.

 

[DavidBC]

Pat, I really can't comment on gun barrels as I never made one.
The one central concept of gun drilling is to rotate the work piece with a stationary drill (1.) But Professional drillers also rotate both the work and the drill (counter-rotate) (2) and most of my work was rotate the drill with stationary work piece (3) .
Each has it's own issues , parameters and inaccuracies. It also seems to be a closed field, or one with "Secret Arts" .
With only the work spinning, you get 10 times greater chance of accuracy versus stationary work as an example ( drift from Centerline is about .0001" per inch versus .001with stationary work)
I have heard of gundrillers straightening barrels after drilling ( making the bore straight and then returning the OD and Tapers ) . but am unaware of any reamer use ,
The real problem to me is doing the rifling ..now that is a skill.

Rich

You are correct it is an art. There are several methods.
1. After you drill the hole and are going to use the hook and scrape method you use 3 reamers to prepare the bore before starting. The 3 reamers are a roughing, a finishing and then a burnishing reamer. The blank with the deep hole is now ready for the rifling. Depending on the number of lands and the depth the rifling head can be passed anything up to 48 times thru the bore. The barrel is then hand lapped and polished to achieve a smooth consistent finish.
2. If you are going to use the hammer forged method the blank with the hole is heated and a male mandrel duplicating the exact sizes and barrel twist is inserted in the hole and the blank is then hammered around the mandrel to for the required rifling and calibre. When finished the mandrel is removed leaving the barrel formed as per calibre and twist required.
3. The most frequently used method is by forcing a small piece of tungsten carbide ground like a projectile to the exact size of the bore and with the depth of the lands and the twist required ground into it. This piece of carbide is pushed thru the hole under high hydraulic pressure. It sizes the bore burnishes it and forms the lands and twist all in one operation. After all these operations have been finished the barrel can then be profiled.
4. Very early shotguns had what you call Demascus barrels. They where made from iron and stell ribbons twisted and welded together. These barrels should be used with black powder paper cartridges only. Putting a modern cartridge in them because of the pressure generated in the chamber causes them to unravel into the strips of metal they were originally made from usually causing drastic injuries to the individual firing them.

You are correct with your statement about barrels been straightened, this is the last operation of manufacturing a barrel especially after heat treating them. It is done by eye, the person straightening them looks down the barrel and slowly looks for a shadow and then places the barrel between 2 vee blocks and by years off experience knows just how much pressure to apply using a hand operated screw press. He repeats this process until there is no shadow.

I hope what I have written will help you understand some of the work that goes into barrel making. I have many books on it and the different methods and tooling required. You can type in barrel making on YouTube and watch barrels being made.

Regards
David

 

[DavidBC]

David, I took a look at your reference posting.
Pretty interesting approach. Not sure I understand the do not withdraw comment ??
Any info on creating the crease in the tube ?
The poster may have some se of this approach.
Please remember, my post is what is done commercially.. hobbiests always find a new way to skin a problem
Rich

 

[Bentwings]

The smaller hole the harder is to drill.
If can use larger drill.
The auto industry has specialized drill press for drilling deep holes.
I could take a day of drill a hole.

Dave

It’s amazing you are found as well as you are. Stainless is hard enough to drill small holes the speed needs to be just right and you need to keep cutting. Once you get a hard spot it’s trouble time. SS work hardens very quickly . Thicker and larger tools you usually can just “ bull your way through but small drills and mills you risk breaking a tool . I YHINK I’d do a “ practice hole “ in mild steel first just to get the process down .
min hog don’s radial engine drawings book he notes a special deep hole drill as the crankshaft is stainless an has deep holes . I don’t remember what was reverse flite or something . There was also a supplier. I’ll see if I can find it.
byron

 

[L98fiero]

Done lots of Gundrilling to 40 " depths from 3/8" to 1" in Diameter and also designed and built a Gun Drill platform /system
I do not want to discourage the poster as sometimes great things are discovered by experimenting and doing things that no one else has done
So let me say a few words about the parameters of these drills.
Gun drills are very frail and made with thinwall steel tubing. The strength is not related to the tubes wall thickness, but to the pressure it operates at. The higher the pressure the more rigid the the drill. the more rigid the drill, the faster the feed rate can be .
Our drills ran at 4,000 PSI (and some small drills -not ours) go to 10,000 PSI. At 4,000 PSI on a 3/4" drill, we would feed at .0005 per revolution ( 800 RPM) .
Part of the pressure is lost due to chip evacuation. at the exit hole to drive chips back to the spindle which may bleed off 25 % of the pressure, so the drill only has 3,000 in our case and the other 1,000 is used to drive the chips out of the hole. The most difficult part is oil control and filtering. You need to collect the oil , then filter it so you do not destroy the high pressure pump...obviously, the higher the pressures, the more sensitive the pump becomes and The smaller the oil system is, the harder it is to do this.
I think gundrills them selves are pretty cheap, but maybe the poster has a weird size that he wishes to make. I don't understand his design , so cannot comment on its operation or considerations. I assume he wants to do this in a lathe, and the small drill means requires very high rotation speeds .

I covered some of the aspects of gundrilling in another post on another thread years ago and you can access it here.

https://bbs.homeshopmachinist.net/forum/general/44496-deep-hole-drilling-101?t=43432
One of the problems of posting is having a college kid thinking he has all the answers with no expeience in the real world , so there is some digression with impossible theory posed by naysayers.. just read my text , to get more gundrilling concepts.
Rich

There are alternatives, not having used them I can only speculate on the effectiveness but they use an air/mist system at standard shop air pressure up to 150 psi and the say it works. Sterling Gun Drills - deep hole drilling,gundrilling,drills,gundrills,gun drills,toolholders,spraymist systems,Twinmaster drills,and drilling accessories.

 

[Richard Carlstedt]

Yes, we tried the air mist approach ..very dangerous IMHO and messy
You have fine chips and coolant mist blowing out at 150 PSI ... a no no in our shop
We had to tent the lathe with poly and that acts as a restriction on viewing work.
You could wear a full face shield I guess..but the chips wound up in our other machine tools and the machinist had gloves and aprons/coveralls
..Could be used for one off I suppose, but not for repetitious work
You could make a collector like they use on normal fluid systems - We made our own , here is a link that shows one . The drill then has slingers on the inside and the collector is held to the work through many different methods while drilling .

https://www.homemadetools.net/homemade-gun-drill-dust-collector
and use a "Wet" Shop Vac to help control the Air/chips/mist/..

The difference in Air systems versus Liquid (normal gun-drilling) is feed rate and surface finish . The air system is low pressure( <1000PSI )which means less rigidity of the drill or lower feed rates and lower pressure means more vibration --which affects surface finish /performance
Then you add the lowest feed rate on the lathe may still be too fast ???
Having a VFD motor on a separate leadscrew drive is an asset as you look at less than .0005" feed rate per revolution
Not insurmountable, but challenges to the home hobbiest

Rich

 

[Rains]

Without the flutes, there is a chance that iron chips will come out, but doing so may damage your drill bit.

 

[Bentwings]

Without the flutes, there is a chance that iron chips will come out, but doing so may damage your drill bit.

ive only used gun drills a few time. Made a few to print in the tool room. Almost always warped in heat treat. Requiring some close precision grinding to make them dead straight . If you can get straight through air or coolant you may be able to get chips to flow . A blind hole may be an issue as noted .
Byron

 

[57mm_M18]

Go to Drill masters Eldorado in milford CT. Talk to these folks about drilling deep holes, they have a lot of man years in drilling and manufacturing of this type of drill. My suggestion is, buy the drill already made by someone that knows the business. Also, have them sharpen the drills for you, it is a skill.