|Home » Forums » CNC » Message||Login|
You are not logged in. Consider these WOODWEB Member advantages:
High feed rate, low ramp angle vs modest feed rate with increased angle4/16
Curious how many use high feed, low ramp angle. Started with recommended settings, but I'm thinking high feed with an angle of 3 degrees or slightly less with a feed of around 4500-5000 mm /m may yield a better product. I'm using alphacam, operation is nested type rectangular rosette in oak/ white oak. Having problems with parallel edges picking up at the corners and blowing out. It isn't economical to use breakout cut, takes too long, would not be profitable. We are already using an end mill to rough out first. Will get exact feed and rpm tommorow.
While your question is about ramp in rates I think there is a lot more here to consider.
I assume you are talking 3" to 6" long sides in 4/4 and/or 5/4 material. Also since you are referring to parallel edges I'm also assuming you have multiple rosettes next to each other out of a single wide board. Is this all correct?
If so then the questions are:
1) What diameter bit in relation to the space between rosettes? Is the bit edge touching side by side rosettes at the same time or is the gap between parts wider than the bit diameter? If wider, how much wider?
2) Upcut or down cut spiral bit? Upcut will lift the parts while downcut will compact the chips in the cut slot which will help to hold the parts in place.
3) Are the rosette corners blowing out when they are not lifting as well as when they are getting lifted off the table?
4) Are you making a full depth cut in one pass? Is the roughing pass full depth or onion skinning? Is the finish cut in one full depth pass? Is the lifting taking place on the roughing pass, finish pass or both? Have you tried tabs on the roughing pass if that is going full depth?
5) What is the hold down system? Bleed board hold down with typical rosette sized parts is actually looking for trouble. Custom made gasketed true vacuum fixtures would be a much better system. The caveat here would be that there could still be room for side shift issues with the small parts.
6) What size blanks are you starting with? 8' long boards for example or 2' to 3' long blanks? Could the blanks themselves be vibrating/shifting and thus adding to the problem?
Lots of questions here but generally I'd say you are on the right track with slowing down the feed rate. However I don't know if changing the entry drop angle will make much of a difference one way or the other. I'm assuming here you are talking a z-drop entry angle vs. an x,y side entry angle.
Also the bit design can have a big impact on this both from the perspective of upcut / downcut and the shear angles of the bit edges. You might find it useful to talk to your bit manufacturer to see if they have any recommendations.
Actually I'm referring to helical tool path. I first use a 3/4 rougher to size out the blanks. I'm using 3/4 inch flat stock. The roughing pass looks good, no grain lift. I 'm leaving 1 mm for the profile bit to clean up, also helical cut with that. Stock is a 5 1/4 x 42" board laid on a piece of maple which is sealed with 2 coats , stock is screw to it from the bottom side tightly, no movement. Machine is pod and rail.. Forgot to get the feed data today.
If these are rectangular shapes program the lines rather than the parts and cut from the corner into the middle.
They make left handed tools and reverse rotating spindles for this reason.
I don't do a lot of solid wood, but my experience has been that the roughing works great but the finishing is a problem.
You could try a chipbreaker bit which may leave thin lines that a quick sanding would get rid of. A 3 flute rougher may work as well the same - then you'd avoid a tool change.
You may not want to spend extra machine time, but at some point it's cheaper than bad parts.
Post a pic.
Rpm is 17000, feed is 2250 mm/ min