Surface finish banding

Help Support HMEM:

DKGrimm

Active Member
Joined
Jan 28, 2021
Messages
28
Reaction score
16
Location
Cedar Rapids, Iowa
Just a curious response from a drop-in to this string: has anyone though about the possibility of a moiré-like pattern -- a beat frequency -- caused by a nonintegral ratio between number of steps in each axis?
 

deepfryed

Member
Joined
Nov 10, 2021
Messages
12
Reaction score
2
Location
Australia
Straightening long slender shafts is a tricky business - I spent years in the shockabsorber business as well as using the rod straightening facilities for straightening (lightly) bent motorcycle fork legs bent in racing mishaps. (don't try fixing badly bent fork legs.)
Using a hydraulic bench or arbor press can only get you so far - you reach a point where it will flex and accomplish nothing and then going just a couple of thou further will bend it the other way - often worse than it was.
Ultimately you have to hit it with a soft hammer or lead thumper - use aluminum supports or covers to strike points if using a steel hammer.
Start over the full length - then half and half - go back to full length - repeat until you get 0.001" TIR
Easy if you have the skill - practice on a similar diameter round barstock first just to get a feel for how hard you need to smite it.

Regards, Ken
Thanks Ken. I'll ask around, but in all likelihood (if it's an hour or more of work) the cost to straighten the leadscrew will be more than what I've paid for a replacement ($100 AUD). It's funny 0.2mm run out doesn't sound like a lot, I expected the saddle gibs to be rigid enough to prevent any lateral movement.
 

deepfryed

Member
Joined
Nov 10, 2021
Messages
12
Reaction score
2
Location
Australia
A quick update for posterity:

1. The whiplash or error is due to a combination of bent leadscrew and incorrect alignment of the bearing block at the far right side. I've adjusted the bearing block to improve the whiplash, also still waiting on the leadscrew replacement. Meanwhile I've made some modifications to make make this much better.
2. I've replaced the cast iron saddle gibs on the front with brass gibs that snug up the saddle in 2 directions, from bottom to top and from front to back. This has helped greatly in reducing the errors and have nearly eliminated the banding issue.

Here's an example part turned using canned radius turning cycles on my controller, not perfect but I'm happy with it for the moment.

IMG_20211227_104752_588.jpg
 

awake

Well-Known Member
Joined
Sep 4, 2019
Messages
1,422
Reaction score
614
Location
North Carolina
Just a curious response from a drop-in to this string: has anyone though about the possibility of a moiré-like pattern -- a beat frequency -- caused by a nonintegral ratio between number of steps in each axis?
I suppose that is moiré-or-less what he has been working with.

:)
 

Latest posts

Top