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L00 backing plate

jgimp69

jgimp69

Active Member
Was asked to machine up a backing plate for a buddies Clausing lathe so he could mount a 3 jaw on it (It only came with a 4 jaw).
Rough machined the plate to about 0.050” over, then cut the tapered bore after tramming the compound slide and finished with the threads.
Wasn’t happy with the finish of the bore, had some chatter I just could not get rid of. Tried everything. Even tried a stone in my air grinder clamped the the tool post. Side note, don’t try that! If it’s a problem, I will just borrow the tool post grinder from work and clean it up.
Used 1045 steel. Machines up nice. Hadn’t used it before.
Going to blue it up on his spindle before I cut the keyway, see how it sits.
Nice project though
 

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jgimp69 said:
had some chatter I just could not get rid of. Tried everything............ .............. ............ ........... Machines up nice. Hadn’t used it before.
Click to expand...

These two statements are incompatible to me. Maybe I'm reading them wrong. What's the story here?
 
Susquatch said:
These two statements are incompatible to me. Maybe I'm reading them wrong. What's the story here?
Click to expand...
Im the common denominator lol.
The outer diameter and facing went great. Threading, beautifully. When I started using the cross slide with boring bar (Dorian MWLNR), I just could not get it to stop chattering. Tried different speeds and feeds, changed inserts, slight adjustments on the tool height. Frustrating to say the least.
 
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jgimp69 said:
Tried different speeds and feeds, changed inserts, slight adjustments on the tool height. Frustrating to say the least.
Click to expand...

Gotcha. Now I understand.

Boring bars can be difficult to tame. Sometimes changing feeds N speeds works, but often it doesn't because neither one directly affects the natural frequency of the bar itself.

Although you didn't mention it, I assume you tried choking up on the length of the bar. Sometimes a strip of lead attached with double sided tape works miracles.

They also sell boring bars with built in damping. = BIG $$$$$$

I've also had good success switching to a HSS bar - not a steel bar with a HSS bit - a honking big bar of HSS! I got one in a KIJIJI haul and love it! No idea how they put the hook in the end of it though. Looks like it was made that way.

Always wanted to try dipping a bar in a thick coat of silicon rubber.
 
Susquatch said:
Gotcha. Now I understand.

Boring bars can be difficult to tame. Sometimes changing feeds N speeds works, but often it doesn't because neither one directly affects the natural frequency of the bar itself.

Although you didn't mention it, I assume you tried choking up on the length of the bar. Sometimes a strip of lead attached with double sided tape works miracles.

They also sell boring bars with built in damping. = BIG $$$$$$

I've also had good success switching to a HSS bar - not a steel bar with a HSS bit - a honking big bar of HSS! I got one in a KIJIJI haul and love it! No idea how they put the hook in the end of it though. Looks like it was made that way.

Always wanted to try dipping a bar in a thick coat of silicon rubber.
Click to expand...
Yeah, I’ve seen those anti chatter bars. I’ve thought about getting one, especially in the smaller size, but the price is hard to swallow. In the past, I have tried slowing the speed and feed right down and using HSS on a bar, I just don’t have one anymore. They are cheap enough and I really should have a few different sizes. Either way, I think that the surface finish should be fine for his purpose, if not I’ll break out the TP grinder.
Never heard of putting lead on it. Or dipping it in silicone for that matter lol
 
I alway use the heaviest bar I can on a bore. My go to is a 1" Accusize bar.
But I have used a tapered bar that started out as 1" and tapered to 5/8" over 5 inches. In my limited understanding of harmonics that would be a hard thing to start a frequency in, and it seemed to be anti chatter for sure.
 
Ironman said:
I alway use the heaviest bar I can on a bore. My go to is a 1" Accusize bar.
But I have used a tapered bar that started out as 1" and tapered to 5/8" over 5 inches. In my limited understanding of harmonics that would be a hard thing to start a frequency in, and it seemed to be anti chatter for sure.
Click to expand...

A bigger fatter bar is a no-brainer. But what happens with a tapered bar? Does a tapered bar really make it better or is it actually worse? What an awesome subject to research. Its easy for me to think of multiple arguments both ways. My off-the-cuff thinking is that the natural frequency of a long cone shaped bar is roughly the same as the midpoint cross section. It probably also has a wider excitement frequency band. Therefore more likely to chatter but at lower amplitude. I'd also expect that all bars vibrate laterally as well as torsionally due to the cutting forces. Any analysis has to address both modes. Logically, it has to be better than the same length bar all the same diameter as at the cutting end. Similarly, it has to be worse than the same length bar all the same diameter as at the base end. But that's just a SWAG.

I bet that a formula exists and that experiments have been done. If not, calculus is probably our friend. Much as I'd LOVE to research it, I am under the bridal microscope getting ready for my youngest sons wedding here at the farm to do that work right now - my bride would kill me if she caught me. But maybe @mbond or @Arbutus or others have first hand knowledge. If not, I'll do it when the festivities are over.
 
jgimp69 said:
In the past, I have tried slowing the speed and feed right down and using HSS on a bar, I just don’t have one anymore.
Click to expand...

I ran into the same issue cutting the taper on a D1-6 plate and the best I could do was turning very slowly (like bull low) using a choked up boring bar and a very carefully ground and polished HSS cutter. The sharper the better. This was for the shallow finish dimension cuts.

IIRC I tried the aluminum insert on steel trick and that wasn’t as good either.

D :cool:
 
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