With good programming, lash (at least consistent lash - and with fancy enough programming, I suppose arbitrary lash) is as little an issue as your ability to measure it - just tell the drive to compensate, and have some sort of homing routine so it has a known point to start compensating from.
There's also the simple approach, which is to always rotate the same direction - just as you were planning to do by hand. If you need to be CCW 1 degree, go CW 359 degrees (or vice versa)
Yeah, I thought of that too. I still want a large bore 4th axis. There was an awesome huge chuck that sold on Ebay recently, but I decided I needed servo drivers for my big mill more than I needed a chuck right now.
"Ecnerwal" wrote
The tooth at the top shows the effect of backlash:
jsw
You might look at my route. I have a servo mounted on an AL plate. Most of the time its bolted to my knee and I run the 4 axis configuration where height tool offsets are done automatically.
Then I unbolt the servo and bolt it to the table. Put my dividing head (with considerable backlash) on beside it with a pulley between. Then I load "CNC with 4rth axis" into the control. I do have to crank the knee table by hand.
I do have a nice 5C collet fixture with nice heavy duty bearings. if the need arises, I'll mount a huge toothed belt pulley to it and write, "CNC control with lathe".
You get the idea.
Karl
Sounds like the story of my life. Only sometimes I have neither.
Now you're getting more advanced. Hobbing involves coordinated motion of two axis at the same time. You'd need a good CNC 4rth axis. The advantage is one cutter does all gears from tiny to rack. I'd start with the involuter cutter idea.
You want to read Ivan Law's book, "gears and gear cutting". there's a section in there on making involute cutters starting with round HSS blanks to make a fly type cutter.
I love my devleig boring bars with removable brazed carbide inserts. I can calculate the exact involute shape and plot it at 50X. Lay a paper cutout on the optical comparator with the 50X scope. Start grinding on the baldor carbide grinder and setting the work in the comparator. Only takes a few minutes to get the involute shape perfect.
Karl
I don't see why it needs coordinated 4th axis motion. Don't see why the table couldn't be advanced manual by my calculation chart method just like using an involute cutter.
I just ordered a copy from Amazon. Interestingly a new copy was cheaper than a used copy. Still a single point "fly" cutter type setup is going to be so sloooooow.
Watch that video, the hob cutters are trapezoid shape. If using your method with this cutter you get something that will look like a timing pulley. if you rotate the blank in unison with the hob set up at an angle you will get an involute gear shape. the advantage of the hob is one cutter makes any number of teeth for that gear type.
True, thank goodness for CNC. Just let it run and do something else. back to that old time or money thing.
Karl
Actualy that's not right. Run a hob against a part that doesn't move and it will end mill it. The hob cutters are on a helix.
Here's the article that i used to draw a gear at 50X:
Just discovered there is an automatic calculator built into CamBam that does involute gears and timing pulleys. Actually I knew there was a gear calculator of some kind in the toolkit, but I never looked at it before. Obviously to use it you need to program backlash compensation in your mill and/or adjust down your backlash adjustments as close as you can. Still, with this you can cut them out of plate with a simple 3 axis CNC mill. Cool beans. Simple profile operation. It even tells you the maximum size end mill you can use.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.