Cutting / Flattening Plenum Board

[mrgadget]

I am slowly in the process of assembling and fixing my bot I purchased used. I emphasize the word s-l-o-w-l-y as I purchased it last year and have just gotten this far. I used the shopbot supplied flattening file as I want to make my machine as accurate as I could. This is actually the second time I have run the file. The first time it produced ridges I could hang my fingernail in. I took the z-axis apart and leveled it using levels and the process outlined by Brady, and now I am not getting those ridges anymore. Success somewhat!! If you rub your hands across the light and dark areas in the photo you can feel waviness or very very tiny rolling hills is best I can do to describe it. Is it possible to reduce this to a flatter surface than this? After this step I want to cut the plenum but I want to get this correct first. Thanks!

Jay Waters
17752

[gerryv]

I've been through this. The thing to remember is that you are dealing with very small variations that may or may not be an issue depending on the type of jobs you'll do and, the diameter of the largest bits you'll use - the larger the bit's cutting diameter, the more it becomes an issue.

What you are describing as rolling hills, albeit subtle, suggest that your Z axis is still not quite perpendicular on either X or Y axis, or both. Do a google search on a process called tramming, which is what machinists do with their milling machines. Their precision requirements are typically a lot tighter than needed for CNC routers but the process is the same.

You will find that some folks suggest using a bent coat hanger or equivalent to make a tramming device and yes, that will work but only to a point. Your average machinist will scoff at this type of tram because it is just not rigid enough and the tip of the hanger or equivalent where it comes in contact with your table is very uneven if cut with pliers or the like so that it reflects light differently as you rotate it, which also throws you off. They are correct.

That does not mean you can't make one up yourself - just that it has to address those issues and must not get shifted when it drags at the low point when slowly rotated by hand (with no power going to the spindle!). The googled explanations should describe what I refer to as the low or drag point and this is also where any flex will work against you. A trick I once saw was to use a good flat, very stiff sanding backing pad for an electric drill with a smooth tipped pin pushed through it on one edge and glued in place so it doesn't slip. Pic. attached. The fellow was using a focused beam flashlight to watch where the high point was once the pin made slight contact.

It is also a good idea to use a known, smooth flat surface that is the same thickness side to side and end to end and at least the diameter of the rotated tram. Bigger is better. Place this on the previously flattened spoil board below the tram.

You can buy very thin either metal or plastic shims at most industrial supply houses that can then be stacked as needed to bring things into tram. My preferred kind are the open ended ones that can be slid in behind the V-Groove roller studs or the bolts holding the router or spindle in place.

[mrgadget]

Thank you so much for the time you took to help me Gerald. I really appreciate it. I've seen some different solutions on the forum here dealing with tramming the z-axis and making some brackets to help accomplish this. Very creative and intuitive indeed!! This had crossed my mind but didn't want to do that at the moment, although I won't rule it out. I guess I'm getting close to cutting (and patience running low) and ready to make sawdust not turn more wrenches! I guess I know I need to keep fine tuning the z-axis, so I might as well resign myself to doing it. By the way, my machine is a PRT Alpha and I surfaced this with a Her-Saf 1.375" insert bit that worked like a champ. Thanks again!!

[coryatjohn]

I used a piece of 10 gauge copper wire about 2' long bent into a Z. Copper is better than a coat hanger because it doesn't have much spring to it. I also had lots of single strand 10 gauge wire hanging around.

To enhance the size of the gap made by the wire to the table, I used a bright flashlight held nearly flat on the table so I could measure the gap using the shadow of the wire. It worked amazingly well. It was easy to eyeball the distance and I got the Z axis to the point where I can see tool marks but no ridges.

[mrgadget]

Thanks John! You guys have given me some good ideas to play around with this weekend when I can have some bot time. I'm sure I have some things laying around the shop I can find to do this. If not....I'll make do like any good 'ol country boy would!! Oh...and I can say that cause I'm guilty as charged!!! Hope you guys have a great day and I'll come back here when it's flat as a flitter!!

[ron_moorehead]

I bought one of these systems a few years ago and have used it to align most of my shop tools including the spindle on the ShopBot. Works great and has mutliply uses.

Deluxe A-Line-It Alignment System

http://www.in-lineindustries.com/a-line-it.html