# Boring A Long Tube



## prasad

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". 
	

		
			
		

		
	



	

		
			
		

		
	
 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


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## Tony Wells

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.


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## kd4gij

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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## Wreck™Wreck

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.


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## John Hasler

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.


Use at least 1" rod.  It's a very simple tool to make.


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## prasad

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


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## joshua43214

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?


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## David VanNorman

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.


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## prasad

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


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## Chipper5783

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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## Tozguy

For boring a 2'' hole to a depth of 4'' it would be much better to use a bar larger than 1/2'' of mild steel. Considering the level of precision you are after it seems to me that you need a more ridgid tool. For example, a 1/2'' square bar would be more ridgid than a round bar.

Or a 1'' round bar can have one end turned to 1/2'' to fit the tool holder but leave the unsupported part at 1'' for rigidity.

Also, do you absolutely need to use the square boring bar holder or can you clamp the boring bar directly in the post as Joshua mentionned?


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## prasad

Tozguy said:


> For boring a 2'' hole to a depth of 4'' it would be much better to use a bar larger than 1/2'' of mild steel. Considering the level of precision you are after it seems to me that you need a more ridgid tool. For example, a 1/2'' square bar would be more ridgid than a round bar.
> 
> Or a 1'' round bar can have one end turned to 1/2'' to fit the tool holder but leave the unsupported part at 1'' for rigidity.
> 
> Also, do you absolutely need to use the square boring bar holder or can you clamp the boring bar directly in the post as Joshua mentionned?




Tozguy

Thanks. I am not boring it much in the real sense. The amount of material I will remove is very small. The bore is already just under 2" and I have to enlarge it very slightly, just enough to let my 2" accessories enter in. So, I can take very small cuts to prevent flexing of the 1/2" boring bar that I want to make/use. I feel it should work. 

True if I have to really cut much more - e.g., enlarging a 1.5" to 2" then I may not use a 1/2" boring bar. 

Any case I will soon share my experience.

Thanks again
Prasad


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## joshua43214

This holder can fit both 1/2" and 3/4 bars. You just drive out the sleeve to use the bigger bar.
The AXA currently shown on the LMS website looks similar to this one.


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## Charles Spencer

If you buy the Shars brand as in the picture it says "Shars" where the others say "China".


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## prasad

joshua43214 said:


> This holder can fit both 1/2" and 3/4 bars. You just drive out the sleeve to use the bigger bar.
> The AXA currently shown on the LMS website looks similar to this one.


No Joshua, 

I can not use boring bar holder of this type. My G4000 has not been modified for QCTP. I still use the good old 4-way tool post. 

Meanwhile I made a long boring bar and ground the tip of the cutting tool bit. Tomorrow I will have to try to hold the tube in the 4-jaw chuck and see if my newly made boring bar will be able to travel the entire length without touching anything.  I hope I can. I keep my fingers crossed.

Thanks again 
Prasad


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## joshua43214

prasad said:


> No Joshua,
> 
> I can not use boring bar holder of this type. My G4000 has not been modified for QCTP. I still use the good old 4-way tool post.
> 
> Meanwhile I made a long boring bar and ground the tip of the cutting tool bit. Tomorrow I will have to try to hold the tube in the 4-jaw chuck and see if my newly made boring bar will be able to travel the entire length without touching anything.  I hope I can. I keep my fingers crossed.
> 
> Thanks again
> Prasad


Doh...
I am so sorry. I just made a stupid assumption.
The 4way will atleast give you a more rigid set up. Good luck getting the hole done.


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## prasad

joshua43214 said:


> <snip>
> The 4way will atleast give you a more rigid set up. Good luck getting the hole done.



Joshua

That is an interesting comment you made. I have been toying with the idea of making a Norman Patent style QCTP.  Can you educate me why a QCTP would be less rigid than 4-way? 

Thanks
Prasad


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## mikey

Prasad, you might want to test this bar on a piece of scrap first. I say that because the physics of boring are about to become reality for you. Not saying you cannot do it with a 1/2" bar; we've all broken the rules and gotten away with it but depending on the cutter you're using it might turn out less than optimal. 

You are using a steel bar, which will flex about twice as much as a similar tool made of carbide; this has to do with the modulus of elasticity of the bar material. Normally, steel can extend in a ratio of about 4:1 (extension: diameter of bar), while carbide can go 8-10:1. The diameter of your steel bar influences deflection to the 4th power, such that a 1/2" bar will deflect 16 times more than a 1" bar at maximum extension, which you are at. Add to this the fact that you are holding this bar in a 4-way post that is not rigid so chatter is a distinct probability. Finally, the cutter itself will alter cutting forces in unknown ways so you cannot predict them.

The bottom line is that you should test your set up first.


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## Wreck™Wreck

mikey said:


> Add to this the fact that you are holding this bar in a 4-way post that is not rigid so chatter is a distinct probability.


I beg to differ.
A four way post will hold the tool just fine, often more accurately and rigidly than a quick change tool post of the same size (the four way is the original quick change, 4 tools indexed by bearing balls, sans easy height adjustment). a right pain in the keester to use however unless you consider shimming the tools every time you use one "fun", I do not.


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## David VanNorman

Make an adapter to hold a 3/4  bar in a piece that  your 4 way will hold.


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## joshua43214

QCTP's have a smaller foot print, the tool carrier hangs out in space only supported by the dovetails in the post, and those dovetails that are prone to rocking. Those fortunate to own an Aloris probably never notice problems, dunno, I can buy a new machine for the cost of an Aloris...

A boring bar held in a 4 way will be applying force directly or near directly down onto the cross slide. The wider foot print and vertical pressure make them more stable. 

It is just simple physics, a 4way tool post is just by it's nature more rigid.
Their downside is that they are just enough of a hassle to set up correctly, that they tend to get set up almost correctly more often. QCTP are just so convenient that any bad is out weighed by the good. Plenty of folks stick with the 4way though


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## mikey

I am well aware of the pros and cons of a 4-way tool post, having used one extensively. However, I disagree that it is the best way to hold a boring bar. This is not just about the stability of the tool post itself. It is about how well the bar is held in the tool holder.

A round bar held in a slot that locks the bar down with screws provides contact at two very small spots on the bar provided that you shim the inside of the slot to bring the screws on center. You must also shim the bar evenly to bring the tip of the cutter 0.005-0.010" above center. In addition, the screws may, and often do, displace the bar, causing misalignment. Given that the tangential forces experienced by the bar tend to twist the bar, this arrangement is the worst way to hold a boring bar.

The most rigid method of holding a boring bar is in a holder that completely encases the circumference of the bar in a finely finished and hardened bore. Ideally, this holder will be 3-4 times the diameter of the bar being held. Screws are then used to tighten the circumference of the holder to rigidly hold the bar in place, thereby reducing vibration and the possibility of the bar moving as it cuts. An example of such a holder is the Aloris 4D; it is not a coincidence that this holder for 3/4" diameter bars is 3" long, finely finished and hardened.

It is well known that a QCTP can easily sustain the cutting forces encountered while boring. I own an Aloris AXA post that holds a 3/4" bar under full extension quite well  but even my little OXA post can handle a 3/8" carbide bar at full extension, 4" deep in a hole. The issue when boring is not just the downward (tangential) pressure like it is with external turning. It is the tangential and radial forces that we have to contend with and a good holder  is the best way to achieve that.

Don't take my word for it. See this article by _Dr. Uwe Heinrich_ of Micro 100:
http://www.ctemag.com/pdf/2005/0512-Boring.pdf


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## British Steel

Nobody going to suggest a between-centres boring bar and clamping the tube in a V-block (suitably shimmed) on the cross-slide? Best there is for a truly cylindrical bore...


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## turnitupper

If you don't want to line bore it, find a piece of rod 1"-1-1/2, doesn't really matter what grade but the bigger the better. mill/grind, angle grind/file one end to fit your tool holder making sure the center of the bar is close to the screws  of your tool holder. Cut off bar to whatever you need . Drill hole at 30-45 degrees  parallel to the tool holder base in end of bar to suit a piece of square HSS tool steel. No need to square off the hole. Put a set screw in top of bar to hold tool. Sharpen tool to suit and cut. Fine tune on scrap first.
John.


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## joshua43214

mikey said:


> I am well aware of the pros and cons of a 4-way tool post, having used one extensively. However, I disagree that it is the best way to hold a boring bar. This is not just about the stability of the tool post itself. It is about how well the bar is held in the tool holder.
> 
> A round bar held in a slot that locks the bar down with screws provides contact at two very small spots on the bar provided that you shim the inside of the slot to bring the screws on center. You must also shim the bar evenly to bring the tip of the cutter 0.005-0.010" above center. In addition, the screws may, and often do, displace the bar, causing misalignment. Given that the tangential forces experienced by the bar tend to twist the bar, this arrangement is the worst way to hold a boring bar.
> 
> The most rigid method of holding a boring bar is in a holder that completely encases the circumference of the bar in a finely finished and hardened bore. Ideally, this holder will be 3-4 times the diameter of the bar being held. Screws are then used to tighten the circumference of the holder to rigidly hold the bar in place, thereby reducing vibration and the possibility of the bar moving as it cuts. An example of such a holder is the Aloris 4D; it is not a coincidence that this holder for 3/4" diameter bars is 3" long, finely finished and hardened.
> 
> It is well known that a QCTP can easily sustain the cutting forces encountered while boring. I own an Aloris AXA post that holds a 3/4" bar under full extension quite well  but even my little OXA post can handle a 3/8" carbide bar at full extension, 4" deep in a hole. The issue when boring is not just the downward (tangential) pressure like it is with external turning. It is the tangential and radial forces that we have to contend with and a good holder  is the best way to achieve that.
> 
> Don't take my word for it. See this article by _Dr. Uwe Heinrich_ of Micro 100:
> http://www.ctemag.com/pdf/2005/0512-Boring.pdf



I never said the 4 way was the best.
I merely said that by it's very nature it is more rigid.

Boring bars for 4 way posts have a square sleeve for clamping, or have flats ground onto them.
As for deflection, if you are deflecting a flat or un-sleeved  3/4" (or even a 1/2") bar in any meaningful way, they you are way past proper torque.



(the set on the right is a Micro 100 set)

I am not sure what your point is. We all know that Aloris and other style QCTP's do the job for boring, and we all know that shimming is a drag (I even pointed that out). None of this changes the points I made above. As for a carbide bar, the OP was pretty clear that he did not want to spend the money on a piece of tool steel for just this job, I think it is safe to say that a carbide bar is also out of the question.

As for Dr. Heinrich, all I can say is be wary of a person who wears a lab coat and writes sales brochures. Those of us that have math degrees know that all we have to do is write a little bit of symbolic math and every one goes "OK, I take your word for it because you are obviously smarter than me." Any time I want my boss to leave me alone, I just start babbling about PDE's or the pros and cons of different ways of arriving at R^2 and she goes away. Seriously, I can just picture a conversation between a shop foreman and a machinist using Dr. Heinrich's math:
Boss: "Uhhhh, Bob, what are you doing?"
Bob: "Setting up the machine for boring."
Boss: "You need a calculator for that?"
Bob: "I have to calculate the modulus of deflection so I know how far above the centerline to set the tool."
Boss: <blank stare>
Bob: "See, the tool will flex down when I start the cut. Not only that, the tool will twist, so I also have to calculate the optimal depth of cut so the tool comes in line when it is under load."
Boss: "Ummm..."
Bob: "I am having a bit of trouble with this though. The optimal depth of cut does not work out with the chip load of my tool when I try to figure feed and speed."
<pregnant silence>
Bob: "I was about to call Dr. Heinrich at Micro 100 and see if he can help me get this straightened out."
Boss: "You're fired."
I suppose that a CNC  machine dedicated to high production output of a single part would be set up like this. But this is a hobby forum, and we tend to use the "cut and adjust" method.
We can spend all day discussing clamping length, smoothness of clamping surface, etc. So we clamp our 3/4" boring bar into a 3" long holder full of confidence that we have a rigid set up. Then we drop the tool holder into a tool post that only has about a 2" diameter contact ring with the cross slide. A chain is only a strong as the weakest link.
A 4 way tool post is substantially larger than a QCTP, and has substantially more contact area with the cross slide. typically, you can also put a much larger tool into a 4 way than into a QCTP. Now, I agree that putting a round tool in a square slot will give poor results some of the time, but this is not the fault of the tool post, it is the fault of the user for not using the right tool.

Personally, I despise the 4way, and use an Aloris style QCTP. I am just not a blind to the fact that I gave up some rigidity for convenience. I have no experience with a real Aloris. Maybe it really is as rigid as a 4 way. I will probably never know, I can buy a used lathe for the price of an Aloris set.


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## John Hasler

mikey said:


> I am well aware of the pros and cons of a 4-way tool post, having used one extensively. However, I disagree that it is the best way to hold a boring bar. This is not just about the stability of the tool post itself. It is about how well the bar is held in the tool holder.


I use a (shop made) 4-way, not having money for fancy stuff.  However, for my larger boring bars I just use a simple split block that entirely replaces the tool post.   It's as easy to make as the boring bar itself and while not perhaps not as convenient as an Aloris I can't imagine how anything more complex could be as rigid.


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## prasad

Guys

I made it and it is done now. The long 1/2" boring tool that I made worked OK. I mounted the aluminum tube on the 3-jaw chuck and centered it to make sure that it ran true within 1 to 1.5 thousandth at the far end. Run out near the chuck was not readable or under 0.001".  Ran the lathe at its slowest speed (I am not sure if low speed was proper but I thought low speed would give me time to react to any "accident").  Mounted my very special boring tool in 4-way tool post and plunged only 1/2 thou for each pass. Sure, I had to be very patient because each pass took a very long time. In the end after about 30 minutes of running time the tube was ready. My accessories fit properly. The 2" eye-pieces fit well. I am happy at the outcome. 

I want to thank everyone for your truly great suggestions. I was lost without them. 

A couple of lessons learnt (by me). 
1. I should do the boring operation before I work on the outside of the tube. I had to be extra careful because I kept it to the end which was a mistake. Next time I will do it first. 
2. Next time I would also make an aluminum collet ring for gripping the tube in the chuck. That would make the operation much easier and risk free. I did use some aluminum shims between the jaws and the aluminum tube. These shims may have created some runout. 
3. I also managed to "get to know" my 3-jaw chuck better. It has a runout of under 0.0005". Made me feel good.

Thank you all,
Prasad


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## kd4gij

1/2" boring bar 5 1/2" deep  .050 per pass.


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## prasad

kd4gij said:


> 1/2" boring bar 5 1/2" deep  .050 per pass.


Hi Martin

True but I could not risk it. I had the tube gripped lightly in the 3-jaw chuck. A little extra force could have moved it. Also all I had to do was enlarge 0.008" in diameter of the tube. I did not want to risk wrecking the piece. 

I will, for sure plunge deeper when I do it on another tube for my next Crayford focuser. In fact I will be making one to replace a crappy plastic Chinese R&P focuser on an iOptron 80mm f/5 refractor soon. 

Thanks
Prasad


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## kd4gij

I didn't think you would take that deep of cut for your project. light cuts and a good  sharp HSS bit and you should be fine. My bar probably a little more ridged than mild steel. Just posted to show 1/2 can work. Good luck. looking forward to seeing how you make out.


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## David VanNorman

I have one of the two piece boring bar holders it handles 3/8 1/2 and 3/4 It is as solid as can be made.


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## prasad

David VanNorman said:


> I have one of the two piece boring bar holders it handles 3/8 1/2 and 3/4 It is as solid as can be made.



A two piece? Can you share a picture or a link where it is sold? 
Thanks
Prasad


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## prasad

kd4gij said:


> I didn't think you would take that deep of cut for your project. light cuts and a good  sharp HSS bit and you should be fine. My bar probably a little more ridged than mild steel. Just posted to show 1/2 can work. Good luck. looking forward to seeing how you make out.



Martin

My work is done for now. I will not start another focuser immediately now because I will now start working on the mirror cell for my 12.5 incher.  

Thanks
Prasad


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## mikey

joshua43214 said:


> I never said the 4 way was the best.
> I merely said that by it's very nature it is more rigid.
> 
> Boring bars for 4 way posts have a square sleeve for clamping, or have flats ground onto them.
> As for deflection, if you are deflecting a flat or un-sleeved  3/4" (or even a 1/2") bar in any meaningful way, they you are way past proper torque.
> 
> 
> 
> (the set on the right is a Micro 100 set)
> 
> I am not sure what your point is. We all know that Aloris and other style QCTP's do the job for boring, and we all know that shimming is a drag (I even pointed that out). None of this changes the points I made above. As for a carbide bar, the OP was pretty clear that he did not want to spend the money on a piece of tool steel for just this job, I think it is safe to say that a carbide bar is also out of the question.
> 
> As for Dr. Heinrich, all I can say is be wary of a person who wears a lab coat and writes sales brochures. Those of us that have math degrees know that all we have to do is write a little bit of symbolic math and every one goes "OK, I take your word for it because you are obviously smarter than me." Any time I want my boss to leave me alone, I just start babbling about PDE's or the pros and cons of different ways of arriving at R^2 and she goes away. Seriously, I can just picture a conversation between a shop foreman and a machinist using Dr. Heinrich's math:
> Boss: "Uhhhh, Bob, what are you doing?"
> Bob: "Setting up the machine for boring."
> Boss: "You need a calculator for that?"
> Bob: "I have to calculate the modulus of deflection so I know how far above the centerline to set the tool."
> Boss: <blank stare>
> Bob: "See, the tool will flex down when I start the cut. Not only that, the tool will twist, so I also have to calculate the optimal depth of cut so the tool comes in line when it is under load."
> Boss: "Ummm..."
> Bob: "I am having a bit of trouble with this though. The optimal depth of cut does not work out with the chip load of my tool when I try to figure feed and speed."
> <pregnant silence>
> Bob: "I was about to call Dr. Heinrich at Micro 100 and see if he can help me get this straightened out."
> Boss: "You're fired."
> I suppose that a CNC  machine dedicated to high production output of a single part would be set up like this. But this is a hobby forum, and we tend to use the "cut and adjust" method.
> We can spend all day discussing clamping length, smoothness of clamping surface, etc. So we clamp our 3/4" boring bar to a 3" long holder full of confidence that we have a rigid set up. Then we drop the tool holder into a tool post that only has about a 2" diameter contact ring with the cross slide. A chain is only a strong as the weakest link.
> A 4 way tool post is substantially larger than a QCTP, and has substantially more contact area with the cross slide. typically, you can also put a much larger tool into a 4 way than into a QCTP. Now, I agree that putting a round tool in a square slot will give poor results some of the time, but this is not the fault of the tool post, it is the fault of the user for not using the right tool.
> 
> Personally, I despise the 4way, and use an Aloris style QCTP. I am just not a blind to the fact that I gave up some rigidity for convenience. I have no experience with a real Aloris. Maybe it really is as rigid as a 4 way. I will probably never know, I can buy a used lathe for the price of an Aloris set.



Sorry for the delayed response - we're dealing with the death of a close family friend.

My point is that a boring bar held at two points of contact is not the most stable arrangement, regardless of the rigidity of the tool post. If you sleeve the bar or otherwise support it then that improves things but as we all agree, it has to be shimmed into proper alignment.I never said a 4 way post won't work; all I said was that he should test the set up before boring into something that already has some work in it. 

The article I linked to is one of the few, if not the only article I've found, that discusses the comparative suitability of the available holder configurations. I found this information interesting and useful so I won't be impugning the guy. I've used all of these holders over the last 25 years or so and have settled on a circumferential holder in a QCTP because it performs the best and damages the bar the least. I've never had the post itself move so while it may not have the footprint or solidity of a 4way post, I don't care. What I do care about is that a solid holder is more important than the bar itself and I know, at least for myself, what that holder is.

In the end, none of this matters. Prasad was able to do the job with the tools at hand and it turned out okay. There are so many variables in boring that testing a set up before boring a piece with a lot of work in it is a worthwhile approach, which is what I intended to convey in the first place.


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## Wreck™Wreck

Did a bit of boring in aluminum tubing today, 3.69" diameter X 6.25" thru using a 2 1/2" Dia. bar with a 432 triangular insert leaving a .150" wall thickness, this is the easy part.
Tomorrow I will put them on plugs and turn the OD to 3.810 +-.005", these parts finish at .060" wall thickness, this may not work at all.




I have a fair choice of tools to use.


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## joshua43214

mikey said:


> Sorry for the delayed response - we're dealing with the death of a close family friend.
> 
> My point is that a boring bar held at two points of contact is not the most stable arrangement, regardless of the rigidity of the tool post. If you sleeve the bar or otherwise support it then that improves things but as we all agree, it has to be shimmed into proper alignment.I never said a 4 way post won't work; all I said was that he should test the set up before boring into something that already has some work in it.
> 
> The article I linked to is one of the few, if not the only article I've found, that discusses the comparative suitability of the available holder configurations. I found this information interesting and useful so I won't be impugning the guy. I've used all of these holders over the last 25 years or so and have settled on a circumferential holder in a QCTP because it performs the best and damages the bar the least. I've never had the post itself move so while it may not have the footprint or solidity of a 4way post, I don't care. What I do care about is that a solid holder is more important than the bar itself and I know, at least for myself, what that holder is.
> 
> In the end, none of this matters. Prasad was able to do the job with the tools at hand and it turned out okay. There are so many variables in boring that testing a set up before boring a piece with a lot of work in it is a worthwhile approach, which is what I intended to convey in the first place.



Sorry to hear about your friend, I understand perfectly. I seem to be losing family members at the rate of 1 every 9 months these last few years. It never gets easy.

I think we agree on the important parts. I do use a QCTP, and I do not ever have an issue with it either. Common sense and proper set up gets the job done.

As for my snipe at the good doctor, I just could not resist. I read peer reviewed papers constantly where the author sounds more like a salesman selling new findings, than a researcher reporting results. I actually write narratives heavily loaded with irony like I did above in my lab reports at times. It flies right over the heads of the PI's, researchers lose their sense of humor somewhere in grad school I think lol.


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## mikey

Thanks, Josh. Here I was, talking about boring while unbeknownst to me he lay in his driveway, bleeding into his brain. No, it never gets easy.


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## prasad

mikey said:


> Sorry for the delayed response - we're dealing with the death of a close family friend.
> 
> My point is that a boring bar held at two points of contact is not the most stable arrangement, regardless of the rigidity of the tool post. If you sleeve the bar or otherwise support it then that improves things but as we all agree, it has to be shimmed into proper alignment.I never said a 4 way post won't work; all I said was that he should test the set up before boring into something that already has some work in it.
> 
> The article I linked to is one of the few, if not the only article I've found, that discusses the comparative suitability of the available holder configurations. I found this information interesting and useful so I won't be impugning the guy. I've used all of these holders over the last 25 years or so and have settled on a circumferential holder in a QCTP because it performs the best and damages the bar the least. I've never had the post itself move so while it may not have the footprint or solidity of a 4way post, I don't care. What I do care about is that a solid holder is more important than the bar itself and I know, at least for myself, what that holder is.
> 
> In the end, none of this matters. Prasad was able to do the job with the tools at hand and it turned out okay. There are so many variables in boring that testing a set up before boring a piece with a lot of work in it is a worthwhile approach, which is what I intended to convey in the first place.



Mikey

Please accept my sincere heartfelt condolences. I know how it feels when a person close passes. Thank you again for all the information and advice. 

Prasad


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## mikey

Thank you, Prasad. I appreciate it.


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## Scruffy

Oops


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## Tony M. Baker

prasad said:


> 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".
> 
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> View attachment 114000
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> 
> 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 is nice looking work. Do you have any drawings of the project


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