Facing backlash issue

[martik777]

Near the end of a facing cut, the last 1/32" or so, the crossfeed jumps forward towards center and I have to backup to get a square face. I assume this is caused from backlash, of which I have about .020.

Is there a trick to overcome this?

 

[Ed Hoc]

martik, It sounds to me that the tool is a little low, assuming you are talking lathe facing cut. The work tries to climb over the tool bit and pulls the 'slop' out of the lead screw. The backlash is a fact of life, unless you have CNC and ballscrews. The tool should be on center as close as possible.

Ed

 

[Tony Wells]

I agree with Ed. Try raising the tool a bit. It should be right on center but not above.

 

[flutedchamber]

Or you could face from the center out. It eliminates all the problems.

 

[Tony Wells]

Well, if the tool is below center, it can't cut all the way to the axis. It will leave something behind at the center with the diameter of twice the amount the tool is below center. Being below center is fine, but try to hold it to just a few thousandths. That still will leave a nib, but not much of one. Facing from the center out will still start at some diameter greater than zero. And it does require a different grind of the tool, since you have to plunge in before you feed out.

 

[flutedchamber]

You can use your standard tool and just angle it towards the chuck a bit more than you would if you were feeding from the outside in. I've used this method with unmodified brazed carbide toolbits with complete success.

Even if you had to modify the toolbit to do so it would be faster, easier and cheaper than replacing a worn screw and nut.

 

[Davo J]

Check it is on centre hight as said above, also check you gibs are tight on both the cross slide and the compound. Sometimes this lets enough flex to allow the tool to go down under the centre and over the other side.

A blunt too will do it as well, because there is a lot more force on it and the tool tip looks for the easy way out.

Dave

 

[martik777]

HSS tool (1/4") was on center but a little dull. They sure don't stay sharp for long.

flutedchamber:

I also angle my "standard" toolbit for various cuts rather than change to the proper bit.

Thanks

 

[Davo J]

Just try not to run them to fast or get them to hot or they will go blunt quick. A HSS tool bit sharpened right should last around an hour before needing touching up, it just depends on the job and the cuts.
You will also find you get a better finish and the tool will last longer if you hone the tool with a oil stone after grinding.
Another thing to consider is the HSS quality. If you are using Chinese ones they don't last as long as good quality and if you can get them with cobalt, even better.

Dave

 

[george wilson]

The CORRECT way to face is to start from the center(though I usually start from the outside!) The advice to start from the center is good,as it will eliminate the problem.

The reason I usually start from the outside is that I can quickly determine the depth of cut needed to clean off,say,a bandsawed piece of large dia. metal. You could do the same by putting your cutter deep enough to clean off the metal by trying it against the outer edge. Note where your compound dial is set so it will clean off all the bandsaw cuts. Then,move to the center of the bar,and move your compound into the rotating metal by that same amount. Then,proceed to face the metal off. Actually,I never face with just 1 cut. I take 2,just in case the uneven depth of cut as the material revolves deflects the tool in and out at all on that initial cut.

I hope this made sense.