Deep Drilling In aluminum block

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kylenlord

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Hi everyone,

A while back I purchased the Martin Ohrndorf V-12 plans. I've been studying them for a while to get an idea of the construction. I found a supply for 7075 aluminum for the crankcase at a reasonable price. One part has me a bit stumped so I'm trying to wrap my head around the problem before considering starting the project.
The main bore is 42mm through the crankcase which is approximately 8 1/2" long. I've been trying to find a 1.5" drill bit to have a starting point for line boring but usually the bits are way too short on unreasonably priced.

At my disposal I have a Bridgeport and a 13x40 lathe. My first thought was mount the block on the carriage and find the right drill bit and mount that in the spindle. Then leave the setup and install a line boring bar to get to the final dimension.

The crankshaft has aluminum bearing supports, which match the 42mm hole diameter and have press fit bearing. The consistency of the holes seems more critical than the dimensionally accuracy as these parts can be made to suit.

Thank you for any feedback,
Kyle
 

Longboy

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The line boring bar tooling determines the minimum size hole needed to start the operation. Will a 3/4 in drill (larger or smaller) reduce your costs and allow the boring bar? Large drills tend to have reduced shanks for half inch chucks and bit extensions can be fabricated to run them thru your 9 inch stock length.
 

petertha

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I have the plans too & wondered the same thing. Pre drilling from both sides would require something with say 4.5" of cutting length considering a typical point. I haven't checked catalogs extensively but that's getting up there for even ~1" pilot hole. If one utilized a reduced shank drill with an extension arbor (blue shade) wouldn't you have to deal with lack of flutes at the end (yellow shade)? The spade insert type shanks look viable but very spendy.
 

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geo

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How about a gun drill or fabricate a version of Dave Wilks large diameter boring bars look him up on you tube.
 

Scott_M

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Taper shank drills are not too expensive here is one from Shars about $25.00
1-1/8"3MT HSS Taper Shank Drill
I have the 1 1/8" 1 1/4" 1 3/8" and 1 1/2" . They are pretty nice drills.
Absolutely make sure the tang is trapped, do not rely on the taper alone to hold this big F'n drill and keep it from turning. :( My tailstock sleeve was not reduced at the end of the taper so I did the set screw mod to keep big drills from turning. One on each side of the tang.

Scott
 

jkimberln

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Hi everyone,

A while back I purchased the Martin Ohrndorf V-12 plans. I've been studying them for a while to get an idea of the construction. I found a supply for 7075 aluminum for the crankcase at a reasonable price. One part has me a bit stumped so I'm trying to wrap my head around the problem before considering starting the project.
The main bore is 42mm through the crankcase which is approximately 8 1/2" long. I've been trying to find a 1.5" drill bit to have a starting point for line boring but usually the bits are way too short on unreasonably priced.

At my disposal I have a Bridgeport and a 13x40 lathe. My first thought was mount the block on the carriage and find the right drill bit and mount that in the spindle. Then leave the setup and install a line boring bar to get to the final dimension.

The crankshaft has aluminum bearing supports, which match the 42mm hole diameter and have press fit bearing. The consistency of the holes seems more critical than the dimensionally accuracy as these parts can be made to suit.

Thank you for any feedback,
Kyle


I think you are going about this exactly right. I had something like this to do and also have a 13 x 36 jet lathe. I made a T-slot table out of a cast iron slab that replaces the top compound and bolted my casting to this. Luckily I had a casting that didn't need drilling. I made a boring bar out of 1" steel with a cutter that was adjustable using a set screw pusher on a carbide round of about 3/16" OD. The boring bar went between centers and was about 2' long. Once the workpiece was aligned, it was easy to get the hole bored straight and to size.

I think you might be pushing it a little to expect a 1 1/2" drill to go straight. Most of these long drills have a 1/2" shank. Personally, I would use no more than a 1 3/8" drill for a pilot hole. In any case make sure the drill point is ground so that drill wander isn't built in right from the start. Even new drills need checking.

BTW, where are you located?
 

SmithDoor

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I have seen bar drill out 4" id x 240 long.
Thay also drill out gun barrels

Dave


Hi everyone,

A while back I purchased the Martin Ohrndorf V-12 plans. I've been studying them for a while to get an idea of the construction. I found a supply for 7075 aluminum for the crankcase at a reasonable price. One part has me a bit stumped so I'm trying to wrap my head around the problem before considering starting the project.
The main bore is 42mm through the crankcase which is approximately 8 1/2" long. I've been trying to find a 1.5" drill bit to have a starting point for line boring but usually the bits are way too short on unreasonably priced.

At my disposal I have a Bridgeport and a 13x40 lathe. My first thought was mount the block on the carriage and find the right drill bit and mount that in the spindle. Then leave the setup and install a line boring bar to get to the final dimension.

The crankshaft has aluminum bearing supports, which match the 42mm hole diameter and have press fit bearing. The consistency of the holes seems more critical than the dimensionally accuracy as these parts can be made to suit.

Thank you for any feedback,
Kyle
 

Mago

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Hi all,
I had this problem when drilling an oil hole in my Offenhauser model.
I needed a drill about2.5mm dia and a hole length about100mm.
I used anew drill of the correct size and ground a scarf on the plain end, then on a length of SS rod of the same dia of the drill ground an identical scarf.
Checked that when brought together there was an approximate match.
Mounted the drill in the lathe sc chuck and the plain rod in the drill chuck in the tail stock.
Brought them together with minimal gap and then silver soldered them together.
carefully cleaned up the joint so that the joint would not bind when drilling.
Drilled carefully and watch for swarf building up in the flutes.
Just one solution, good luck.

Mago
 

Badhippie

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Hello
Use a taper shank bit that match’s your tail stock taper. Drill somewhat close to final size but leave yourself enough room to correct any alignment problems that may be encountered from drilling. Then line bore to final size while correcting any alignment issues.
Thanks
Tom
 

awake

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I have the plans too & wondered the same thing. Pre drilling from both sides would require something with say 4.5" of cutting length considering a typical point. I haven't checked catalogs extensively but that's getting up there for even ~1" pilot hole. If one utilized a reduced shank drill with an extension arbor (blue shade) wouldn't you have to deal with lack of flutes at the end (yellow shade)? The spade insert type shanks look viable but very spendy.

I have drilled past the point where the flutes disappear into the hole. The key is very short pecks at that point - drill just a bit, pull out and unpack the chips from the flute, repeat.
 

kylenlord

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Awesome, thank you everyone for the feedback!

I think from what I gather, I'll grab at minimum a 1"x 9 or 12" drill and plan to drill from the headstock with the piece mounted on the carriage. Then line bore to the finished dimensions. Pethertha, I'm glad to hear that I wasn't the only one pondering this issue. A friend of mine does have a taper adapter that would let me put a mt bill into my headstock. I'll see him tomorrow and find out what he has.

Jkimberin, I am in chilly Rhode Island. Hoping the weather will be picking up so I can finally get back out into the garage.

Thanks again everyone
Kyle
 

Richard Carlstedt

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Kyle, Your line boring on the Lathe is exactly the way to do it.
Great choice on using 7075 !
You can save time and money using the Bridgeport to rough out the hole.
I am not familiar with the block you are purchasing , but it needs to be square (parallel surfaces) and the hole centered between two sides. Mount a angle plate ( or two angles) and clamp the block to the angle plate with a stop on one side for center control and drill and then flip the block and drill . The 5 inch stroke on the quill should get your holes joined. Be sure to LOCK the table, cross-slide and knee, to assure a common center line !. I would not go above 1-1/8" before moving to the Lathe .
I spent 10 years doing gun-drilling when I worked and although you won't need a gundrill, please know that for the straightest possible holes, start with a Ball Endmill . Do not centerdrill , use the ball endmill and you get much straighter holes to start . So say .750 start and go as deep as you can then follow with your regular drills , then go larger using the previous holes as a guide and flip
With the angle plate and stop for location, you can drill, flip and drill, and then change the drill and repeat.
Rich

PS let me add that on the last pass, before Lathe work if the hole is not broke through, you and stop with the drill in the hole and pull some of the shank out of the chuck and then do the break through
OR, raise the knee for the final push
 

petertha

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A few months ago I started modelling the V12 as a bit of lofty diversion. Today I had a thought that maybe the inside cavity could be milled out as a first op, leaving only the 2 ends to drill & bore. But just eye-balling, looks like the center hole must be done first. In all honesty I just glanced atthe construction notes here & there, maybe he makes specific reference. I needed a bit of diversion from the Ohrndorf 5-cyl radial I'm on the proverbial home stretch. Just falling way behind on posting LOL. Look forward to your V12 build whenever it commences.

Somewhat related, have you landed on some good ideas of a line boring bar assembly for the task? Or is the classic adjustable HSS bit the current plan?
 

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Iampappabear

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Just one comment on selling deep holes on a Bridgeport is that the swarf tends to fall back into the hole, you can never get all the swarf out. Having drilled holes 5/8" diameter and 50" deep, the flatter the point of the drill, the less it wanders.
 
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Hi all,
I had this problem when drilling an oil hole in my Offenhauser model.
I needed a drill about2.5mm dia and a hole length about100mm.
I used anew drill of the correct size and ground a scarf on the plain end, then on a length of SS rod of the same dia of the drill ground an identical scarf.
Checked that when brought together there was an approximate match.
Mounted the drill in the lathe sc chuck and the plain rod in the drill chuck in the tail stock.
Brought them together with minimal gap and then silver soldered them together.
carefully cleaned up the joint so that the joint would not bind when drilling.
Drilled carefully and watch for swarf building up in the flutes.
Just one solution, good luck.

Mago
I learned and ran gun drill machines when I was in a job shop. Drilling 1/8 up to 2 1/4 holes sometimes 20 inches deep. Main problem I had was coolant pressure to remove chips. If Drilling it's right about the pecking depth. I agree with you about this.
 

Bentwings

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A few months ago I started modelling the V12 as a bit of lofty diversion. Today I had a thought that maybe the inside cavity could be milled out as a first op, leaving only the 2 ends to drill & bore. But just eye-balling, looks like the center hole must be done first. In all honesty I just glanced atthe construction notes here & there, maybe he makes specific reference. I needed a bit of diversion from the Ohrndorf 5-cyl radial I'm on the proverbial home stretch. Just falling way behind on posting LOL. Look forward to your V12 build whenever it commences.

Somewhat related, have you landed on some good ideas of a line boring bar assembly for the task? Or is the classic adjustable HSS bit the current plan?
I think McMaster Carr has fun drills for reasonable price.
 

Bentwings

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Hi everyone,

A while back I purchased the Martin Ohrndorf V-12 plans. I've been studying them for a while to get an idea of the construction. I found a supply for 7075 aluminum for the crankcase at a reasonable price. One part has me a bit stumped so I'm trying to wrap my head around the problem before considering starting the project.
The main bore is 42mm through the crankcase which is approximately 8 1/2" long. I've been trying to find a 1.5" drill bit to have a starting point for line boring but usually the bits are way too short on unreasonably priced.

At my disposal I have a Bridgeport and a 13x40 lathe. My first thought was mount the block on the carriage and find the right drill bit and mount that in the spindle. Then leave the setup and install a line boring bar to get to the final dimension.

The crankshaft has aluminum bearing supports, which match the 42mm hole diameter and have press fit bearing. The consistency of the holes seems more critical than the dimensionally accuracy as these parts can be made to suit.

Thank you for any feedback,
Kyle
Look up blonde hacks. She is a great machinist . She did a line bore operation on her small lathe she did bump the tail stock but she goes into how she fixed it. I’ve seen some big line boring but not done small stuff. The Bridgeport should give you nearly all you need. Wish I had one . Don’t be afraid to make your own tool bit and bearing assembly. It just slows the total operation down but really nice when you are done
 

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