Pocket Inconsistency Photos

[sevans]

Hey all, I just thought I'd post some photos to give a better understanding of what's happening in my previous post. What tha #$%$^????
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[dana_swift]

It looks like Z axis play in your router. That is much more than I get when planing horizontal surfaces. I still get tool marks. Also be sure to check your router is mounted vertically, if it pure vertical it could leave traces like that.

Good luck

Dana

[Brady Watson]

Is your Z pinion tight? Greased? Worn? Nobody can tell if theirs is worn or not...you just replace it. If the Z isn't greased, then you definately need a new one.

-B

[sevans]

This machine is so new, I could not imagine needing a new pinion. It is greased. Any other suggestions? Don't know if it is tight or not...will be back with this info.

[sevans]

No Play in Z

[GlenP]

Hey Sarah, what type of machine do you have standard or alpha? Is you table glued down or screwed down. My machine leaves the same marks and I only have the table screwed down. Upon asking some of the experienced botters out there I need to remove my sheets from the table and glue instead of just screwing down the second sheet. I am curious if yours is glued down then I may have more issues to resolve this problem as well.

[sevans]

Hey Glen,

I have quite a complex array of materials on my table actually. I began this endeavor with the idea that I would not have a vacuum hold down system. So here goes, I attached a 3/4" sheet of Birch Cabinet Grade Plywood to the frame using the supplied carriage bolts and recommended locations just as the manual described. I mounted a 3/4" sheet of MDF (unsurfaced) on top of cabinet grade with countersunk screws app. 16" apart all over. Then I glued down a 3/4" sheet of MDF on top of that. Next I decided to implement a vacuum hold down. I cut the plenum into that top sheet of MDF and applied a 1/2" sheet of MDF to that (siliconed around edges as suggested). I'd say that I could easily lose 3/4" of material on the table. Nevertheless, the plenum was glued with wood glue which I rolled on with foam rollers to get good even coating. Still I'm having this problem and no one person has yet to diagnose. "I don't know" is the most frequent answer. I'm beginning to wonder if this is the sort of thing that I will have to cater designing to. I don't want to, but at this point there isn't much of a choice. Over, Sarah

[Brady Watson]

"I mounted a 3/4" sheet of MDF (unsurfaced) on top of cabinet grade with countersunk screws app. 16" apart all over." <---- There's your problem!

When I 1st set up my Bot, I screwed a sheet of MDF from underneath the table every 6" thinking 'that'll do it'...It was a good solid year before I realized (after walking ON the table and hearing the creaking) that I got just how much the table was moving, and why I was getting the kind of cuts you are getting. ONLY after gluing down a sheet of Medex (like MDF but water resistant) and eliminating all screws did my spoilboard become stable. It was a huge revelation & since then I have been telling people not to screw their spoilboard down, but glue it.

It's probably worth the time & effort to redo your spoilboard/vacuum setup now that you have a better idea of what your needs are...it sucks, I know...but sure beats sanding out machining marks!

I went to another Botter's place one time that had no more than 10 screws holding down the entire spoilboard to the base board. He couldn't understand why his cuts were so inconsistent...after pulling off the top sheet, piles upon piles of acrylic, plywood and other kinds of swarf and sawdust came falling out, like a stuffed closet from a Bugs Bunny cartoon...Glue that puppy down!

-B

[GlenP]

Sarah, just as Brady says I think you need to remove back down to the first sheet and glue the second sheet on. Even glueing the third sheet after screwing on the second leave room for the table to move and give problems. Yes pain in the you know what, but I if you plan on doing area clearing alot its going to be worth it. What type of machine do you have, Standard or alpha?

[sevans]

I have a Standard Shopbot.
I gotta say that I'm finally feeling something now. Fortunately I have a little break coming up and I'd really like to try re-building the surface as you guys have recommended. I truly appreciate this information as well as the sympathy. I do plan to do alot of pocketing. In fact, it's the main reason why I bought the machine. I will try this out and post again to let you know if it works. Is it best to do the bottom sheet (Cabinet Grade), and then 3/4" MDF as the plenum....Glued? Then the bleeder? Oh yeah, do you guys silicone the bleeder down? Someone suggested to me at Shopbot only to silicone the outer edge of bleeder. Just curious as to how everybody else is settiing up. Thanks again!

[Gary Campbell]

Sarah..
We suffered thru some of the same problems that you are experiencing now. There are really only 2 areas that can cause your problem. One as I alluded to in your other post and has been elaborated on in this one is the table/bleeder/spoilboard system. Along with inconsistent material heights, an unstable cutting surface will allow the material to move up or down as vacuum increases/decreases during removal of material.

It is sometimes very difficult to diagnose these problems because we dont realize how great of a visual impact a .010" difference will make during a surfacing or pocketing operation. This problem is compounded by the fact that .010" movement is almost undetectable to the naked eye. Especially in the middle of a spoilboard.

I was able in time, to virtually eliminate the problem by making absolutely sure, using dial indicators that the spoilboard was not flexing. That only solved half the problem. We still had some "edge dig in" when cutting outer profiles after a raster clearance. This was caused by grain differences pulling the Z in different directions laterally. Even tho I would have bet good money that my Z was tight and true, I found that in the areas that had been used the most I had a few thousandths play. I was able to remove that play with a few shims and the Z adjustments. Now that that has been fixed I am able to use a 2.5" bit at 4+ ips anywhere on the table and in any direction and get very good results.

Take your time and hunt down this problem 1 step at a time and I am sure you will have good results. Virtually all the info you need is posted on this forum. Your machine is capable of very accurate work. It is up to us, as the operators to keep it adjusted and maintained. Good Luck!
Gary

[steve4460]

HI Sarah
In the begining I had the same problem . Do you have a PC router on this bot ?.
There is a plastic sleve in that mounting , and if you don;t have that realy tight then it moves up and down . My problem went away after just tightening up that mounting .

Bot on

[sevans]

I am using a spindle with mine.

[paco]

I had a similar problem. Happen to be the cross support that were flexing under the vacuum hold down force. I upgrade to 2X3X1/4 C channel. Only a dial reveal the problem which was happening after half an hour running the vacuum hold down.

You might have a different problem but I thought I should mention what was my problem and what was my solution... don't give up!

[w1cam]

Another note on the Vacuum hold down system, I gave up spending time on makeing new jigs for my larger work. After a long search I found a cheep solution. There is a guy on Ebay that sells a set of four clamps for 25 bucks and they work great. It seems he has a bit of a following. For that kind of money, it's not worth my time to invent new hold down jigs. The larger the piece of material the better they work. Not so great at real small stuff like 2x2 in. but at that size no vacuum hold down is strong enough. I also ordered a set of his double sided clamps to play with. If you are interested check it out. Search user dcad100 on Ebay.

Well, back to work,
Catch you later