I’m trying to make a sign for a family member and I just cannot get a good finish on the bottom of the carve.
For reference, I’m using a journeyman x50 with Makita router and no 3rd rail. I’m using a bits & bits 1/4" short compression bit #425-CM250-SF (changes at .12") and 4/4 white oak.
First, I tried running the sign in one pass at .2 depth, 120ipm and the router set at roughly 15000 rpm. There was a lot of chatter so I stopped that run and reconfigured the file to run at 70ipm and changed the router to roughly 18000 rpm. There were very noticable ridges and I wasn’t happy with it. See pic:
I figured I pushed too hard and so I ran another finishing pass at the same 70 ipm and 18000 rpm, at an additional depth of .02. this cleaned up a lot of the problem areas but still left clear tool marks and swirls and tear out, see pic:
The bit is new and carbide so I don’t think it’s a dull bit. Maybe I’ve chosen the wrong bit entirely. Maybe my table/spoil board/sign are deflecting? Would that happen on such a shallow finish pass? My table is a torsion box, very very stiff. My spoil board is simple MDF.
Does anyone see any issues with my setup? Am I still running too fast? I feel like running that slow at .02 would be clean as a whistle but it’s just not good enough.
Am I expecting too much? I could sand (probably will) but I really need to minimize sanding because the board is already stained prior to carving and I don’t want to mess up the finish.
Alright, if you’re all trammed up, and the fact your feeds and speeds seem pretty reasonable, I’d lean one of two ways. One is that the poor bottom finish is caused by a loose bit, but you seem pretty up on things and likely wouldn’t make that mistake. But everyone has a brain fart on occasion, so can’t hurt to check.
The other thing I can think is that the router or bit itself might be in rough shape. Do they have a lot of hours on them / is this problem fairly new or have you had this issue from day 1?
Tool path wise, you could add a finish pass at a couple thou deep to get that clean bottom. Adds a bit of time to the cut, but it’ll eliminate your chatter and major height issues if everything is tight and trammed.
How is the sign held down? Since there are some passes on the bottom that look deeper than others I ask: Could there be any springiness in the center of the board? If not then I would be checking the nc code to make sure the Z level is holding steady at the bottom and not varying - could be a tolerance setting in the CAM.
Yes the deeper passes are very ragged, but not the slightly higher passes. Makes me think the board was lifting up under roughing and those areas never cleaned up with the finishing pass. I would rub pencil over the deeper areas and run the finish pass again a little deeper. If the pencil disappears but it still comes out uneven on the bottom the you have got to check the hold down method, nc code and cutter sharpness.
The work is held down with 3 strips of xfasten tape. There are no tool changes, this is all using the same compression bit.
I have a suspicion that there is some deflection happening between my spoil board and table, I just didn’t think an .02 finish pass would put enough down force on the piece to deflect a 4/4 piece of oak and 3/4 MDF but I will do some more testing tomorrow.
The pencil trick is a great idea, I’ll give that a shot first thing. I had not considered that the upcut function of the bit may be lifting the workpiece, that would explain some things if that were happening, very interesting thought.
katie,
I would tend to think the tape is “expanding” slightly due to the upcut portion of the bit. If you are using V-carve, set your last pass depth to .002" instead of .02" and see if that helps. You are really trying to clean up instead of getting more depth.
Also, if you have the room for some outside hold down around the border of the sign, that helps too.
I’m having the same troubles as you and asked about it here. Just sending you to more info. I haven’t had the opportunity to try anything yet. I’ll follow what happens in this thread…I hope my link works. yay, it worked!
I would be inclined to agree with this. I suspect there is a bit of lift going on. I would be very curious to know what the results are if you do a finishing pass using a downcut bit to clean up the bottom (just to see if it exhibits the same symptoms).
Here is a project that I have on my Foreman now. You can see the roughing pass on the lower left side and the finish pass on the upper right. This is a difference of only .003 inches, we normally don’t think of such a small amount being all that valuable, but one look says otherwise. Roughing was with a 1/4" upcut End Mill, depth of .125" per pass which is super conservative and at 200 ipm, rastering on a 45 degree angle. The finish is 1/16 tapered ball nose, with no depth limit, and 9% stepover, again at 200 ipm, which is also conservative (should have gone 300-350 ipm), but really the plunge is the biggest constraint, mine is also 200, but should have been more. Do notice, since I was using an upcut, I screwed it down in 5 or so places around the edge, tape wouldn’t be too useful here.
I have a tool setter, so as part of the home sequence, it measures the last bit length from the previous file, I then use the touch plate to establish the Z for the file. This is different from those who don’t have a tool setter, as it requires a 2 step process. I then rewind and it directs me to change to the correct bit number (if it is different from the last file), it then goes back to the bit setter, touches it, and then fires the spindle and begins the cut. Once that bit is complete, it returns over the bit setter and directs a tool change, once that is changed, I press cycle start, and it measures the new bit on the tool setter and goes to work again.
You don’t have to save separate files for different bits anymore, it generates one large file with all the bits and sequence embedded in the single file. You just follow the prompt for tool changes and press cycle start only.
OH! I just realized you were responding to NewsVan, not my pic.
What thickness of xfasten tape are you using? I’ve run into an issue similar to this before where I discovered that the tape I was using was too “soft” and would compress during finishing operations leading to me having to do some extra sanding to clean up the swirl marks etc. Since then I stopped using double sided tape alone and always now provide an extra couple of clamps to eliminate and extra compression that could occur.
