Roller Hold Downs

[thewoodcrafter]

I was milling some hardwood boards todays and found it hard to hold down warped board.

Has anyone made a roller hold down system?
I have seen them on large CNC machines used by furniture manufacturers to hold down the odd shaped part they cut.

I was thinking of trying to set this up. I have a ball screw Z that should be strong enough. The roller should run close to the bit, should have an adjustable tension spring and should be removable.

Any thoughts or comments?

[myxpykalix]

I'm not sure, as i understand your description, if this will work good. The reason i say that is, with my experience cutting some carvings from thick wood what i have experienced is as you rough cut out the bulk of the material it tends to want to curl up from the ends. I experienced tha same effect with warped wood after glue up.
Have you ever seen anyone rolling out pie crust with a roller and it tends to curl up past the pressure point? Or like a rocking chair?

My feeling is that having a roller holddown like you describe would do basically the same thing.
What i have done as a holdown method to eliminate this is this.
I lay my piece on the table and notch out of a 2x4 the size of the piece to fit in. Then i take a bessy clamp on top and bottom to squeeze pressure on the side of the piece. Then i clamp the bessy's down to the table. Then i take scrap mdf and screw it down on the top face edge of the 2x4 to hold the material from curling upwwards. Sorry for the lousy picture but thats all i had. I think this method would work better than what you describe...but hey, i could be wrong, it wouldn't be the first time!


514

[Brady Watson]

Roger,
The device you are talking about is called a pressure foot. I doubt that your Z axis will have enough torque to be effective without losing steps or stalling. Your best bet is to setup 1/8" holes in your part file that will clear the cutting tool & your parts, and do a drilling routine on them. Then, use screws to hold the board to the spoilboard. Vacuum can also be used, but you'll need to make a custom 'mask' of sorts to keep the vacuum from leaking out & popping up the entire board.

-B

[thewoodcrafter]

Ahh, no one has done this.

I am making some fluted pilasters with a bead around the outside edge.
I am also trying to add a bead to the outside edge of cabinet doors. My door supplier charges $15 each for these.

Soooooo, no place for holes in this material.
I did squeeze the pieces across the bed between fixed scrap screwed down and an adjustable piece. Then just tapped the work piece down flat on the table. Worked O.K. Some of the long pilasters just did not want to stay down. You tap down on one end and the other would pop up.

Anyway I thought some kind of rolling foot would come in handy for the odd ball quick hold downs.
I think I will do some testing with the Z and springs to see if this will work.

[Brady Watson]

Roger,
I built & have used a pressure foot on my machine before. It worked OK for some things...not all, and you run the risk of marking the piece up with roller marks if you don't get the durometer of the wheel correct. The pressure foot has since been cannibalized for it's parts and tossed in the trash...

Not even taking the Z axis into consideration, you are going to lift the entire X car, Y car or both off of their tracks if you put any substantial amount of pressure on the foot. In my opinion, I wouldn't even bother with a pressure foot. Read some of the articles on vacuum and make a jig to hold the parts down. The jig/fixture bolts/screws to the table and vacuum holds the piece to the jig. As long as you put the material on the pod/jig/fixture with the crown UP you should be fine. If you are not familiar with vacuum and what it can do when used correctly, it would be worth it for you to do some experimentation in your own shop to come up with some fixtures that work well for the type of things that you cut. Before I started using and testing vacuum hold down methods, I thought it was all a load of malarky...now it's the method of choice 95% of the time.

-B

[conceptmachine]

Roger,
I have been looking into a roller holdown as well,as brady said don't use your z axis or the x car for support you will get into trouble.what i had in mind was use the C channel or aluminum extrusion depending on what model bot you have for mounting the roller guide.then use the x carriage to move the roller,use some sort of screw ,spring setup for applying pressure,and try and keep the rollers as close to the spindle as posible.keep in mind this is just a theory i have not tried this yet but when time permits i will give it a try
shawn

[oddcoach]

I Have had good luck attaching glue blocks to the sides of the piece and then screwing the blocks to the table. i have used hot melt the old fashoned wax kind and titebonds new perfoma both worked well when i was in a hurry. if you have time use regular wood glue and put some brown paper bag in between the part and the block. later the blocks can be poped off with a chisel with no wood tearout
john

[stevem]

I’ve been using a pressure foot since I purchased my Bot in 04, with great success. Most of what I cut is sheet plastic, sometimes two layers at a time (can’t do that with vaccum). The 48 X 96 sheets are anchored to the table with three screws on one short end and the pressure foot that is part of the dust collection system is the only other hold down mechanism.

The pressure foot is shaped like a donut that has been placed on a table and sliced horizontally. It is attached to the dust collection chute and pressure is applied with three small springs that are adjustable for tension and height. The material is UHMWPE and slides along without leaving any marks whatsoever, although it seems to work best on flat surfaces (not necessarily smooth surfaces).

[thewoodcrafter]

Brady,
I use a vacuum table for sheet goods and vacuum pods for some other things now. Your right vacuum is good for 95% of things that come along. I just thought a roller may be useful for other odd ball things. And anything to save time.

Shawn,
I like your idea of, I guess, a separate X car for the roller setup. May work.

[thewoodcrafter]

Steve,
Got any pictures of the setup?