Boring a bearing journal vrs reaming

[RSG]

So it seems as though most people I talk to bore their bearing journals instead of reaming them like I do. Whats the best way - ream or bore to final dia.?

Some background, last winter I made a floating reamer holder and from the tests it appeared to be good but now, when put into actual use I'm finding it's producing tapered holes - a few tenths over at the opening and almost a thou at the back. This is horrible, I was doing a better job when I just chucked the reamer on the tailstock.

Currently I drill, bore then final ream. I don't feel like I am capable of boring to final dia with any accuracy and it may be due to a variety of reasons such as incorrect insert geometry, rack angle, boring bar alloy.....I don't know!

If anyone has any tips I'm all ears as this seems to be the last thing in building reels that eludes me.

Thanks in advance.

[Mr Ron]

No best way. It's whatever works.

[Rich_Carlstedt]

You might say :

Reaming follows the hole and the material and is subjected to it's holder
Boring follows the quill

Your result shows lateral pressure on the reamer IMHO, and your floating reamer tool is very suspect.
You may not have Axial parallelism
If it is a "V" Block style for different sized reamers , mark the V with blueing , and chuck a dowel pin in the spindle with 0,0 TIR
and carefully touch the V mount to look for high spot.

I find we take too much for granted in this hobby. Going for accuracy requires a whole different approach.
I ran a Die shop for years and we took nothing for granted. For example :

You buy a new drill chuck and arbor for your lathe.
Mark the very top of your tailstock quill at the opening with some lacquer(nail polish) with a small dot
Mount your drill chuck to the arbor and chuck a dowel pin in the chuck and then mount the two in your tailstock.
Now put a indicator in the lathe chuck and indicate the dowel pin - mark the exact top of the chuck with magic marker and record the error
from the indicator. Now remove the chuck/arbor and rotate it 90 and recheck. What you will find with all such work is that ONE point
is the most accurate for "that assembly " MARK the top of the arbor to match . If you separate the arbor and chuck do it again
Rich

[pete]

"We take too much for granted in this hobby" Human nature I suppose, but wow Rich's statement couldn't be more accurate imo. If you don't actually check first and verify anything is in fact correct it's a guess only that it might be. And he's talking about checks made in commercial shop where the equipment is larger, has much more mass and for the most part far better geometry built in by the manufacturer for it's true alignment than what most of us might have. And I'd certainly agree that floating reamer holder has one or more issues, something isn't staying pointed directly at the head stock as it should. His thought about that axial alignment is definitely where I'd start first. But just in case I'd also lightly spin and indicate that reamer on both ends in the reverse direction of it's normal cutting rotation so you don't damage it on a couple of V blocks to be 100% sure it's not very slightly bent to rule that out.

Since I haven't seen exactly how your reamer holder is arranged this is only a best guess this might even work. Got any ground pin type material to use as a known straight and round test bar around your shop Ron? I gut any computer printers I come across and save the shafting out of them since it's always real straight and round because it has to be for the job it's doing. It's already hard as hell so not much use as small part stock, but there dirt cheap as smaller diameter test bar material. Get whatever you can find and know is straight mounted in that floating reamer holder and indicate it's side and top along the Z axis. It's still only a static check and may not 100% show exactly what's going on under cutting conditions. But you need to start somewhere. Just remember that gravity is working against you so I'd expect to see at least some test bar bending or sag along the top the further out you are from the reamer holder. It's also human nature to assume a misalignment is constant and probably only on one axis. It could be a variable combination of both and in any direction in your case.

For your reel bearings and on a manual lathe I think your drill, bore and ream is likely the best and most consistent method since your making multiples and require interchangeable parts. The boring gets the hole round and straight so the reamer should follow that, and the reaming gets you the repeatable size as well as probably a better overall surface finish. It's how I'd choose to do it. Fwiw I'll add I've seen some making up either a quick change tool holder or a separate tool block mounted to the cross slide for holding drills and reamers. And even more doing so when the lathe has a dro with a tool memory for exact repeatable positioning just by calling up the tool number. That all sounds a whole lot better than it works in practice when your trying for low 10ths like you are and using axial cutting tools. What there forgetting is all the clearances between the lathe bed and the cutting tools. Each one of those is going to move and twist in the opposite direction an unknown and variable amount. For roughing it would work fine, for what your doing it won't without multiple test cuts and compensation added to correct for those variables. From batch to batch for your reels that would be an almost an unworkable pita. It's also why lathe turrets were invented. Btw, how's your turret project progressing?

[RSG]

Thanks for the detailed replies Rich and Pete! Always appreciated.

Rich, I'll have to take some time to digest your analysis but I think I get the gist if it.

Pete, thanks for the insight. I will have to do the checks and see what the outcome is.

In the past when I just chucked the reamer in the tailstock I got good results. They would fluctuate some but not by much. I was able to run a hand reamer through that my friend ground for me two tenths over size to clean it up. I thought by using this floating reamer holder that I might increase repeatability and accuracy but apparently not. now for these reels anyway I'll need to get fancy and either add some sleeve retainer or score the journals to get the bearing to fit snug.

I looked into getting a solid carbide boring bar 12mm dia x 4.5" and the cost blew me away at $400! A bit steep for what it is.....

[Harold_V]

I've never been a fan of reamers, although I used them extensively in tool making (for dowel pins).
If you want a hole on location, round, straight, and on size, bore. Under all but ideal conditions, those features are difficult to establish with reamers.

Holding size when boring, especially in aluminum, assuming it's a good machining grade, is easy. It just takes practice, pretty much like any other machining operation. I confess, it is slower than reaming.

H

[RSG]

Well I guess I'll just have to learn how to do it then!

[Harold_V]

Well I guess I'll just have to learn how to do it then!

Alternately, you can bore, leaving only a thou or so, then ream for size. Assuming your reamer is on center, or can seek center easily, that often yields acceptable and reliable results.

Key here is to limit how much the reamer must remove, and if it is free to seek center. Grip the reamer by only a fraction (¼) of an inch, so the cutting end can wander easily. The limited cut will readily center the reamer. The risk here is the possibility of a slight bell mouth (and often chatter), as the reamer seeks center.

I may have made mention before that I used a 3/8" reamer for a large number of holes when I built the face plates for the light switches for the low voltage control lighting system I installed in our house. The 3/8" holes had to be straight and round. Location was not critical, but easily established because I made the plates on my CNC mill.

To avoid chatter and bell mouth on entry, I ran the reamer at a relatively high speed, but feed rate was excessive (something like 20"/minute). Both of them were established by trial and error. Net result? Round and straight holes, no bell mouth, smooth finish and straight holes. The rapid feed rate overcame the chatter upon entry of the reamer to the hole. A perfect result for the push buttons that would reside in the holes.

Reamers can work----there's just no guarantee. That's why I like boring.

H

[RSG]

Thanks for the comments Harold.

While I think I can learn the skills of boring to size I don't think my lathe is capable. Before I made that floating (or not) reamer holder my journals were acceptable IMO. They did have a bit of taper but so little that I could run a hand reamer through by hand to correct it. I'll either have to go back to that, see if I can fix the floating reamer holder or work on my boring to size skills .

With that said can anyone tell me what the correct carbide insert is for boring aluminium?

[GlennW]

What size bore?

These if you have a bar that will accept them and fit in the bore.

https://tormach.com/carbide-insert-ccgt-2151-36065.html

Not necessarily this brand, but this style and size. Either 21.51 or better yet, a 21.50.5 (smaller corner radius)

[RSG]

Thanks Glenn!

I am currently looking for a new boring bar so I'll keep an eye for one that excepts those inserts or similar...One thing I have noticed is boring bars have a fair amount of negative rake which I'm sure has to do with chatter but would it help to try to find one with the least amount possible?

[GlennW]

You still want it to cut on center. The "negative" you refer to just aids in front relief.

Look for a SCLCR boring bar.