1st Table Flattening - Need Experienced Eye Feedback

[gerryv]

Hi All,

I've posted three pictures of our first effort at table flattening on a used PRT I bought a while back. As mentioned in the comments, the 3D look is really mostly an optical illusion caused by burn marks from a combination of operator "newbieness" and a horrible old 1.75" wide tool bit.

As you can see there is a fair amount of wandering and variation. We have some thoughts on the causes but would rather get feedback from those who have experience in this area before we jump to conclusions. -

It is clear (not in the grainy pics) that we'll need to tram the router but we'll archives on that before asking about that.

I posted the pictures under User CP/Pictures & Albums/GerryV's 1st Table Flattening Results. hope this works as I've never posted pic's before.

Thanks much in advance.
Gerry V

[myxpykalix]

Gerald,
just below where you type in your text you will see a button for "manage attachments". Before you upload your post you click on that, go to your picture location and add your picture and it looks like what you see here. People aren't going to go searching way back in the bowels of this site for a pic i'm afraid so repost your question with the pics attached here.

[gerryv]

Thanks Jack! That seems to have worked :-)

[ken_rychlik]

yep, router is not level with the table.

[michael_schwartz]

With the machine powered up, grab a hold of anything you can and shake it down to see what may be loose. I check each axis quickly, each time I power up the machine.

Make sure nothing is binding causing loss of steps.

If you didn't level/square the table, and adjust the X rails thoroughly get a PRT manual and go through the entire setup.

[gc3]

oooooohhh that is ugly. :eek:

[GlenP]

Hey Gerald. Send me an email later tonight or tomorrow. I am on my phone but looks like the stepover for bit is larger than the bit diameter as well. Very ugly and nasty.
I can drop down if you need me to.

[gerryv]

Hi Glen,
We first ran it at 10% stepover (which I assume means 90% new cut per pass) for the full table which is what is showing in the photo's. We later ran about 20% of the table at 50% step over which looked a little better but the vertical misalignment of the Z was still obvious (easily seen and felt with a fingernail) so we stopped.

I'm hoping some of the guys will overlook the apparent but not actual "humps", likely caused by heat from the dull and chipped old bit and possibly wrong speed setting on the PC router, and comment on possible causes of the wandering. Looking closely at the long shot pic, you may be able to see that there is a relatively straight line running along the X within the much more wavey outer reaches of the cuts. This is what leads me to think that the lift-off or air cutting on the high side of the Z misalignment is accentuated by the bit diameter. But I'm basing these "best guesses" on basic geometry, not experience so need the advise.

My "guess" is that even a slight misalignment of the Z would result in a multiplying of the effect. In this case, the effect I'm referring to would be that when one of the rails (in this case the right one) becomes even slightly higher than the corresponding height of the other (left) rail, the lift-off or air-cutting of the outer reach of the planing bit will be X times greater than the rail height increase due to even a modest skew on the Z axis. The wider the bit, the more enhanced the variation.

Glen, I'd be very happy to have you come by; lunch is on me as you were a great help when we fired it up for the first time :-)

First though, maybe someone can recommend a good planing bit and a suitable router speed setting as I'm pretty sure that has a lot to do with the burn marks on the big-box store grade MDF.

Sorry for rambling; any other thoughts anyone?

[gerryv]

Thanks guys,

Kenneth, thanks much for the confirmation.

Michael, I never got one of those manuals when I bought the machine so kind of working blind because I only see the newer PRS manual offered on the SB site. I'll call them to see if one is available for download.

Gene, you've such a gentle way with words haha (but you're certainly right :eek:

Glen, separate response posted.

Thanks again guys! Any further thoughts anyone, based on my followup response to Glen?

[ken_rychlik]

I ended up taking all of the inner rollers out of the Y car and making a bearing hold down for the side opposite the Y motor. I used a bearing and spring to simulate the same pressure being applied on the motor side.

I'm not sure, but it very well may be your y car is not adjusted well, or needs something like I did on mine. Grab the Y car opposite the motor and see if you can shake it up and down or back and forth with the control box turned on and motors engaged.

[myxpykalix]

try this bit for your table flattening bit:
http://www.magnate.net/index.cfm?event=showProductGroup&theID=136

2704 or 2705

[danhamm]

2707 would do it in a hurry,

[gerryv]

Thanks for the feedback. I'm very happy with the progress so far. A comparison between this and previous pics I think shows why.

Even after adjustments the bit was still burning the MDF so it was canned in favour of a somewhat cheepo 3/4" bit, as that was the best choice on hand and we have no local supply house for these. No more burning so it was sharp at least.

The Z was indeed way off perpendicular on both the X and Y axes. As can be seen, the cut lines are all now much more parallel rather than wandering. There is still a little bit of a convex look to the cuts showing down the X. In fact, although they don't show on the Y due to lighting and shooting angle, they are the same there. I believe this is due to that fact that I was not able to bring the Z completely perpendicular on the Y axis using with the Z mounting bolts. But, I may be able to take this last small bit of misalignment out by adjusting the eccentric V rollers on the Z.

I also now have my rails ground and honed to within about 1.5 thou variation in terms of height but still need to do a little more to bring the 45 degree side faces that the V rollers actually contact into tighter tolerances. It's pretty eay going because these are not hardened rails.

As suggested, there was indeed slop on some axes - lots actually. The turnbuckle/spring assembly on the Y was barely tight allowing for a good 3/16" play there. Tightening the turnbuckle took care of that. Less of an issue on the X but also improved the same way so now both X and Y no longer budge when given a real good shove in either direction. The Z still has about 1/8th of vertical play so I need to figure out how to tighten it. I'l inspect the pinion gear tomorrow to see if it's loose or worn as I can't see any other way to eliminate that. Any suggestions?

Once I'm as far as I think I can go, I'm thinking I'll cut a series of circles and squares in a sheet of something (ply/MDF/other?) around different areas of the table with the cut file set for an onionskin (I think that's what it's called) to see how these adjustments translate into good results - does this make sense or should I do something else:confused:

Once again, any advise would be much appreciated. Thanks.

[kubotaman]

Gerald I have found in the past to make your spindle or router perpendicular to the tabe in X and Y axis is to use the Wixey gauge. You stick it on a long shaft of a bit or shaft and you turn it in both directions and see exactely how much you have to make adjustments. You can get it exactely perp' to the table!

[chiloquinruss]

On my Z I loosened the bolts and then used some very thin shims behind the spindle and then re-tightned the bolts. Russ