Boring A Long Tube

prasad

prasad

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Guys

I have one last boring operation to perform on an aluminum tube for my Crayford style focuser. Photo of my 99% finished Crayford focuser (minus anodizing) is below and the tube in question is at the top. It is about 4" long and has a rough ID of 2". DSCN0364-1.jpg My lathe is Grizzly G4000 and the longest boring bar can stick into the aluminum tube to a depth of about 2.75". The real boring operation to be done is very little. I just need to enlarge the bore to accept a 2" astronomical eyepiece or a 2" adapter. Since my longest boring bar is not long enough I guess after completing the boring operation from one end of the tube I will have to turn the tube around and mount it the other way to continue the operation from the other end. I want to achieve uniform bore without a perceptible step over the entire length on the bore.

I am not sure if I will be able achieve it to truly centered on the chuck when I turn it around to continue boring from the other end. Also, how will I know that I have arrived at the same diameter as I got when I did the boring from the other end? I am lost. Hence this post. I am seeking your advice.

My equipment: G4000 9x19 lathe - unmodified (i.e., I use the original 4-way tool post)
Chuck#1: Original 4" 3-jaw with internal and external jaws
Chuck#2: 6" 4-jaw independent jaw chuck (LMS) and a set of soft covers on top of jaws to prevent denting of aluminum material
Boring bar set: 1/2" shank carbide tipped set of from LMS with holder to suit.

Thank you guys,
Prasad
AB3EH
Wynnewood PA
 
That's not really a deep bore for 2". I think you should stop and make yourself a bar. That should be done in one operation. Be careful also that you do not chuck too hard on it. Aluminum will crush easily and result in an out of round bore once removed from the chuck.

If you have brazing capability, you can simply braze a scrap carbide insert onto a rod and grind to suit. It's a one time use item, so it doesn't need to be fancy.
 
Sounds like a good excuse to buy a new tool. But if that isn't in the budget now. You can make a boring bar to do the job. Just need a piece of mild steel rod that will fit in your 4 way tp cross drill a 1/4" hole in one end for a 1/4" tool bit and a set screw to hold it.

Here is a link to give some ideas.

http://hobby-machinist.com/threads/home-made-hss-boring-bar.27005/
 
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Bore through in one shot Prasad, 4" depth in a 2" bore is the easiest operation that that you have done so far, if needed buy a suitable boring bar.
The last operations are the ones that cost the most if done incorrectly, you already have many hours invested in this project so do not make a mistake on the last OP.
Any general lathe tool that you by will be used again in the future, aside from threading tools.
 
kd4gij said:
Sounds like a good excuse to buy a new tool. But if that isn't in the budget now. You can make a boring bar to do the job. Just need a piece of mild steel rod that will fit in your 4 way tp cross drill a 1/4" hole in one end for a 1/4" tool bit and a set screw to hold it.
Click to expand...
Use at least 1" rod. It's a very simple tool to make.
 
Thank you everyone, this is a great idea for me. I have mild steel rods and HSS tool bits. I should be able to make on quickly. I will try it with a 1/2" rod because it will readily enter my boring bar holder which fits my 4-way. Using any larger diameter will involve more work which I do not want at this moment.

I will post the result soon,
Thanks again
Prasad
AB3EH
 
1/2" rod is a bit small for 4". give it a shot and see if it works though.

The tool does not need to be round, and it does not need to fit in your boring bar holder. It can be any shape or size that fits inside the rough bore, and only need to be able to fit the tool post.

Does you boring bar holder not have a knock out sleeve for accepting 3/4" bars?
 
I have a 3/4 " bar with a 45 deg and a 90 and the 1/4 " in the 90 is just held with a set screw with a open end I've used it for years. Works great.
 
Hi Joshua

Most of my work has been aluminum. I have plenty of stock in aluminum material but not much of steel. I had ordered a few mild steel 1/2" and 1/4" rods for some project that never took off. So 1/2" is the only mild steel rod I have that I can use for now. I will try cutting in very small steps to minimize flexing of the tool.

I am not sure what you mean by knock out sleeve. The boring bar holder I have came from LMS. It is a square piece with a 1/2" dia hole that accepts 1/2" shank boring bars. On one side it has a slot.

Thanks
Prasad
 
I'll add my encouragement to what others have said. Boring operations are a core competency for lathe operation. Whether for this job, or future tasks, you need to be able to perform most any operation on a component inside diameter, that you perform on the outside diameter. Of course there are numerous tooling arrangements you can purchase. There are also several very good home built designs for boring bars, holders, tool posts, . . .
 
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