5'x5' 15"z ballscrew router frame has come together

[landmark]

I thought I would post a pic of my new machine as it is finally taking shape. The y axis is dual drive with preloaded precision ground screws and rides on IKO 25mm rails with two long blocks per side. The x is a Adept slide that I picked up from HRG surplus for $275. The z axis is a THK KR 46 precision grade slide. I had drew up all the connecting brackets for the y axis and had them water jet cut out of 3/4" plate aluminum. This was buy far the most expensive part. I have about $600 in machining costs, but it had to be done. It will be servo drive, using teknic sst-1500 drives and teknic servos and have a colombo 5hp 24000rpm spindle. I've gotten everything for this router from surplus yards or ebay. I have about $1200 in the frame materials, $600 in machining and 1200 in my spindle and vfd. This was going to be a traditional gantry design but I became concerned about making the gantry too heavy and there being to much flex with such large z axis. So last minute I changed my design . I'll post for pict when I can.

[Northboy]

Very nice!

A bit of concern about flex for a heavy cut with such a long Z, but it looks like a nice machine indeed.

Cheers!

Northboy

[landmark]

Thanks,
I thought about adding more to the x axis in an effort to sure it up like a torsion box but I was really concerned about the weight. To add a torsion box I felt like I would have had to raise the gantry up and the x axis slide is heavy enough without sides and added brackets.

Anyone have any thoughts on or experience with counter balancing the weight of the spindle on the back of the z axis to even out the center of gravity? My spindle and z axis plate will weight in at 40 lbs. I'm worryed that 40 lbs moving up and down quickly will create to much rocking

heres some More pics

[CarveOne]

Very nice!

A bit of concern about flex for a heavy cut with such a long Z, but it looks like a nice machine indeed.

Cheers!

Northboy

In looking at the long Z axis in the two photos, it appears to me that the gantry height will limit the actual useful travel to something much less than the full length of travel. If the router is moved to the lowest position it will be below the table surface. If it is raised any higher than than the lowest physical non-moving part of the Z axis it serves no useful cutting purpose. (It may make tool changes easier though) Is this observation true Landmark, or is there something that I'm not seeing?

Adding counterweight will just make the gantry that much heavier. I'm not convinced that it will gain you anything. You have kept the router as close to the gantry beam as you reasonably can. The beam appears to be plenty stiff as far as twist is concerned. Counterbalancing the weight will do little to resist cutter side loading, which can sometimes be a more significant torsional load.

Nice looking machine so far Landmark. The angle plate casting is a nice touch.

CarveOne

[landmark]

Northboy,
Thanks for you observations it's good to have someone confirm those aspects of my design. The z axis actually has mountible mounitng positions it can be adjusted up and down by 5" incraments. I can also adjust the distance between the z slides mounting blocks and increase or decrease the travel. So I should be able to maxinmize the distance between the blocks and get the right travel. The big down side to the za axis is the small contact area it has with the x axis.

[CNCMAN172]

I am also working on a 5' x 5' router table with a precision slide for the Z axis. I noticed you are planning on using a nice spindle as well. I have a new Colombo 7.5HP and it is very heavy. I used THK 35mm slides for X, 25mm slides for Y, and the precision slide for Z. The Z unit is probably 20" long and I would ultimately like 6-8 inches clearance under the spindle. I am working on the Y axis support design right now and worry that my 11" cantileaver with the heavy spindle will be a challenge. I am attaching the cad drawing and have used a beam straight across similar to what you did as an initial test to check the rails and they are smooth as glass. My table is 3" steel tubing welded and the table top is 3/4" aluminum. I have been buying stuff for this build for over three years and just started the build. After examing the forum looking at various designs I am thinking about making more of a triangle looking Y support plate in an attempt to keep the weight near the center of the two large bearing blocks on each side. The current cad drawing shows the bearings spaced 10" apart for stability, but this design was using Y supports with more of a right triagle approach. Just curious to get your comments. I will be watching you build with great interest. thanks



CNCMAN172
Russ

[landmark]

Russ
Your machine sound like it will be very nice. I would have loved to do welded steel but it was out of my technical reach. Looking at you plans I might suggest flippinf the gantry supports around so they sweep back. This is a good way to move the center of gravity back and get it closer to the center of your slide blocks. I got a lot of good advide from this website, it helped remind me of forces I was trying to design for. http://www.cncroutersource.com/do-it...NC-router.html

Since it seems like you are going to be building your x axis from structual aluminum you may want to consider a designing a torsion box into your gantry like this these plans do. http://www.machinetoolcamp.com/Gallery.htm
If I hadn't found a prebuilt x axis this is the design I would have used. I still would have liked to use it but with the weight of my slide plus additional framing for the box I was worried I'd be making it to heavy.
Good luck

Scott

[CNCMAN172]

Landmark,
Thanks for the links, the first one especially. I love how they walk through the Force and Moment calculations. I am going to model this and determine the optimal bearing spacing, spindle height, etc. The 7.5HP Colombo spindle weights 57 pounds so it is massive. I aligned the heavy duty rails on top of the aluminum rails using a dial indicator attached to the bearings, so I could ensure the bearings were perfectly parallel to the aluminum rails. Using a longer jig to align both sides proved a great way to make sure everything stayed perfectly parallel. With a beam attached across the span bolted to the bearings is never racked no matter where I pulled, however no real weight or force was being applied.

I looked at the photos of the routers that used the extrusion to make a torsion box, however those really did not look like traditional torsion boxes. The extrusion I am using is very heavy 4080 and it will have 1/4 aluminum plates bolted to the back on each end to keep things from skewing. The ballscrew runs down the middle so I could not put extrusion stuts for added rigidity. I am not locked into my current design and will examine the swept back Y axis mounts you suggested. I had already modeled this but was still not happy with the design. The site you provided with the analysis will help me refine my next design attempt. I plan on using 3/4" aluminum for the Supports for the Gantry ends.

Thanks for you help and I welcome any other suggestions.

CNCMAN172
Russ