Cut path problem

[dehrlich]

I ran a project today, new coin bank pattern for Christmas. Anyway the cut bit kinda went crazy on one specific part as you can see in the pic. The rest of the pattern came out fine, just this one side of one piece. What would cause this? Tracking roller problem? I always use two layers of tape and it's pine so nice and soft. Never had a problem before. Any ideas?

82594

[fwharris]

Yes a tracking problem.

[bergerud]

That looks like the infamous stair stepping problem many have had.

[dehrlich]

Any solution or just one of those things? Haven't had this one before

[fwharris]

Any solution or just one of those things? Haven't had this one before

The guys at CarveWright say to cut it in one pass..

[bergerud]

Single pass cutting is not something I do or would recommend. Of course cutting in a single pass will eliminate stair stepping! The question is: will it be the right size? The answer, I think, is no. If there is a tracking problem, even though there is no stair stepping, there is still a tracking problem!

My theory is that the tracking problem is caused by resonant vibration. Certain vibrations from the cutting bit confuse the brass roller encoder. When this occurs, tracking is taken over by the x motor encoder. Without the constant correcting from the brass roller encoder, the x tracking goes off.

The only solutions I have found are to keep the cutting path as far away from the brass roller as possible. (You may notice that the poor tracking seems to occur during the cut along the edge by the brass roller.) My carrier base seems to have solved the problem for me.

[fwharris]

Single pass cutting is not something I do or would recommend. Of course cutting in a single pass will eliminate stair stepping! The question is: will it be the right size? The answer, I think, is no. If there is a tracking problem, even though there is no stair stepping, there is still a tracking problem!

My theory is that the tracking problem is caused by resonant vibration. Certain vibrations from the cutting bit confuse the brass roller encoder. When this occurs, tracking is taken over by the x motor encoder. Without the constant correcting from the brass roller encoder, the x tracking goes off.

The only solutions I have found are to keep the cutting path as far away from the brass roller as possible. (You may notice that the poor tracking seems to occur during the cut along the edge by the brass roller.) My carrier base seems to have solved the problem for me.


It would be good to know what edge he did have his problem on. It would also be good to see a bigger picture of the full carve and cut.

I recall you brining your theory up on another discussion on the stair stepping and multi pass vs one pass cutting. I would not discount it one bit. I've had the stair stepping/tracking issue on several cuts but have plenty without it as well. I have one sled I use for carving 1/2" boards. Depending on what edge I install on the brass roller it will track of about 1/8" away for the squaring plate when moving to the right. The other edge will stay nice and tight to the squaring plate.

[bergerud]

I've had the stair stepping/tracking issue on several cuts but have plenty without it as well.

It was the same with me. Every once in awhile, a project ruined with the cutout. Cutout roulette. I think it is a serious problem because it is so discouraging for the user to, after hours of carving, have a project ruined only minutes from the end.

I no longer do cutouts down on the belts. I now always use a carrier base which gets the board up away from the brass roller. So far I have dodged the bullet with this.

[fwharris]

The majority of my work is done on some type of jig or carrier board as well, got to save that 7" of wood.

[DianMayfield]

The guys at CarveWright say to cut it in one pass..

I had heard that at this year's conference. I came home and started a 1/2" cutout and that bit broke within the first 2 minutes. Never again for me!

(yes, the bit was brand new, as I was a bit skeptical)

[fwharris]

I had heard that at this year's conference. I came home and started a 1/2" cutout and that bit broke within the first 2 minutes. Never again for me!

(yes, the bit was brand new, as I was a bit skeptical)

That happened to me on my first try with the 3/16" bit. If I am cutting out patterns, like Christmas ornaments, I always use the feather tool so the carve will remove enough area around the pattern. This allows me to cut it out in one pass. If I am making up a plaque or sign that has straight edges that is carved on a larger board I will use my table saw to cut it down to size.

[bergerud]

One must be very careful when cutting out patterns. Cutouts go clockwise around patterns and that means that the cutting bit climb mills on the pattern side. If there is no wood on the other side and the cut is full depth, it is easy to snap a cutting bit. (A lesson I learned with the cutting bit that came with the machine!)

[Digitalwoodshop]

Lots of theories.... Interesting.....

My take is that the board is loosing contact with the brass roller for just a few seconds hence the repeat of the stair step.

Masking tape even 2 strips locking the board to the brass roller making masking tape rack and pinion.

Making sure you have 4 inches of un cut wood staying under the front roller.

I even tape a 4 inch board when I am extra frugal... FrugAL.... :)

AL

[DianMayfield]

Al, while I know you probably have stock in 3M, I have followed your golden(tape) rule since my first tracking error 3 years ago. Every project, every board. It has served me very well :)

I have had more than a couple stair step issues. Almost always in the X direction. I find the most common denominator was the newness of the bit. I did a three pass this weekend on a 4 foot board, and it only had as much as a fine sanding sponge will take off. Brand new bit. A bit with 6hrs on it will get me a stair set almost a 16th between first and last pass. Can that little bit of drag cause the stair, yet not trigger an adjustment by the machine in the X tracking? Don't know.

[SteveNelson46]

There are many theories. In my case, I have never had a problem with stair stepping. I have even left only .375" on the tracking roller side so the compression roller doesn't drop and have never had an issue that I didn't cause. Even with multiple passes. This was made really clear on the round Veggie Tray I made awhile back. I tried to make the tray as large as possible and didn't leave much wood on the tracking roller side. It came out okay though. Maybe I just got lucky and have one of the semi-really good machines.

EDIT: Okay, now that I've said that the damned thing will probably break.

[fwharris]

EDIT: Okay, now that I've said that the damned thing will probably break.

Been there done that!

[fwharris]

One must be very careful when cutting out patterns. Cutouts go clockwise around patterns and that means that the cutting bit climb mills on the pattern side. If there is no wood on the other side and the cut is full depth, it is easy to snap a cutting bit. (A lesson I learned with the cutting bit that came with the machine!)

I just got done (well sort of) with close to a 40 hour run of Christmas ornaments out of 1/2" boards. Most of them did have at least a 1/4" feather but a few did not and all were cut at full depth. This is a bit different than full depth on 3/4" boards but those that I have done I always use a feather around the patterns with a full depth cut and have not had any issue.

The only cut out bits I have broken was back in the QC days.

[normrichards]

I had heard that at this year's conference. I came home and started a 1/2" cutout and that bit broke within the first 2 minutes. Never again for me!

(yes, the bit was brand new, as I was a bit skeptical)

I usually use 3/4 to 1 inch boards and I never cut in one pass always .250 increments. When I do get stair stepping which is rare it is usually that my masking tape is getting old (I always use a sled) . Or that my piece shifted on the sled. I have been wanting to build Berg's carrier base but just have not gotten around to it.

[Digitalwoodshop]

Al, while I know you probably have stock in 3M, I have followed your golden(tape) rule since my first tracking error 3 years ago. Every project, every board. It has served me very well :)

I have had more than a couple stair step issues. Almost always in the X direction. I find the most common denominator was the newness of the bit. I did a three pass this weekend on a 4 foot board, and it only had as much as a fine sanding sponge will take off. Brand new bit. A bit with 6hrs on it will get me a stair set almost a 16th between first and last pass. Can that little bit of drag cause the stair, yet not trigger an adjustment by the machine in the X tracking? Don't know.

I agree Bit Health is important too... A Dull bit would need to push harder on the board leading to stair stepping... I remember when I was trying to cut the plastic tags before I learned the trick to lock the feed rate into 1st gear I could see the machine pushing the bit faster than it could cut.... Leading to poor cuts and sometimes the tag would pop off the carrier as I was using double stick tape and no tabs. Once I lied to the machine and locked it in first gear, the 1/16th end mill left a smooth edge and didn't force the cut.

AL