My First CNC Machine, Mr. Chips

[Mr.Chips]

After MUCH reading and study from so many builders and designs I have finally put the mechanical portions together. There are too many people to thank for all the advice and the design tidbits I have plagiarized to finally arrive at this point. And yes this is my first machine, plan to use it to build an aluminum framed design with a movable gantry. One other factor that came to bare is that, how do you say… I am cheap, frugal…. And I let the good parts I found dictate the machine size as far as the X and Z axis are concerned. I did fine two good Thomson twin bearings at the recycle yard but the shaft was bent, I think I can use them for the Y axis of the 2nd machine, if I can find shafts at a good price, they are the full round design rather than the supported type which I would have perfered.

Because I have very limited skills in metal work, and my desire to make it as rigid as possible the gantry sides and cross piece are made using two layers of ¾” MDF. With the cross pieces mortised through the inner layer of MDF. Everything on the gantry was glued and screwed. It is HEAVY, but rigid.

Like everyone I wanted a machine that had as small of a foot print as possible and the largest work space, sounds reasonable to me, and dozens of other builders. This machine started it’s long life (evidenced by numerous holes) as a movable gantry, this impossibility soon became apparent when I mounted the gantry on the ¾” gas pipe rails (GPR) and supported by a four way adjustable bearing drilled and cut from a cutting board. This forced me to change the design to a movable table. This is not a bad choice as far as the function of the machine is concerned. The heaviest thing I will be moving around on the table will be a plate of aluminum big enough to make a side piece of the gantry for CNC #2. Yea I know famous last words.

The base of the machine is made from one layer of ¾” MDF. The table I was building it on wasn’t very level so I used three pieces of 2” square steel tubing as a flat building plane. The end pieces are two layers of ¾” MDF, the inner one being stacked drilled at one time to insure the rails were parallel. Because the rails are so long I placed a piece of MDF under them in the center, and will place other pieces on the sides of the rails to reduce spreading. I was surprised at how little pressure it takes to flex this pipe. The pieces of wood on each side of the gantry running the full length were oriented with the annular rings running up and down this is a much more rigid orientation. I will add another one on each side for additional rigidity. The gantry is screwed to the base and has pieces of MDF on each side to further insure rigidity. Yea I know I’m obsessed with this rigidity thing.

Thank you all again for freely sharing your ideas and time in getting me this far. Be forewarned as soon as I am making chips I will be calling on you all for advise with the software and how they interact/interface with the machine. Currently I am planning on using TurboCNC.

Specifications/Parts:
Over all size: 36” X 66”
Usable table cutting area: 22” X 28”
Z Travel 5½”
X Axis rails 1” shaft with Thomson like bearings. Used …………………………….. $10
Z Axis rails ¾” shaft with Thomson like bearings. Used …………………………… $10
Not used on this machine 1” Thomson Twin bearings. Used …………...…………..…. $2
Y Axis rails (gas pipe) ¾” ID (1” OD) …………………………………………….… $17
Y Axis roller skate bearings 608 ZZ C3 Ebay from a Irvine CA distributor …….….. $16
Controllers (3) XS-3525/8S-1 from Xylotex …………………………………………$120
Stepper Motors 116 oz/in from Xylotex ……………………………………………... $60
Aluminum plate from Austin recycle center 0.68 per lb
Drive screws ½” 10 Cannot lay my hands on receipt ………………..………Aprox. $45

Here is an overall photo. Please see 2nd posting for questions I have about the alignment.

[Mr.Chips]

Below are the readings that were measured on the table right after assemble. Measurements were taken from a grid that was 20” X 24” as shown on the drawing. From these readings I plan to place three steel cross braces under the table and bring up the center -0.038” and the two -0.015” readings and shim the -0.021” to be closer to Zero, then route the entire surface flat.

Is this reasonable?

Thanks
Hager

[Hobbiest]

Looks great. can't wait to see what it can do!

[balsaman]

Looks great! Sounds reasonable. For 2D cutting it's ok to be out a little. I would be mopre concerned about the perpendicularity (word?) of the y versus the x axis.

Eric

[limbo]

Looking really really great! Very clean built.

Greetings,
John

[Mr.Chips]

Eric,
Checked the perpendicularity (word?) this afternoon by mounting a pen to the router post and locking the table and moving the router mount across the table drawing one leg of the triangle.
Then locked the router mount on the X asis and moved the table, drawing the 2nd leg of the triangle.

Used a starrett metric steel ruler.
Marked X leg at 400mm, the Y leg at 500mm.
Measured the third leg and it was 640mm long.
This works out to an angle of 89.94 should have been 90.0.

This is pretty close. I saw a CNC software where it allowed you to plug in this information and it would compensate the angle error when cutting.

Does CNCTurbo have this feature?
Hager

[anoel]

Work it out physically (shims and adjustments)... You'll be glad you did later.

[balsaman]

No, Tcnc doesn't do that for you.

Eric

[Mr.Chips]

Nathan,
I figure I got lucky with an angle of 89.94 deg.
Do you really think it is worth it to try and correct that 0.06 deg error?
Would have to shift the X axis shafts less than 0.5mm on one end.
Meaby I have to do this.
Would like some comments.
Thanks
Hager

[balsaman]

What are you making? It's up to you. Can you live with it?

Don't be discouraged. Get it finished and moving. you can twaek it any time.

Eric

[Carver]

Hi Hager, Really nice job.

Yes it is worth the trouble.
Anything you cut later that has to work with anything else you cut will double the apparent problem.

Even the softwares that compensate for this usually don't do you any good if you simply want to take the proven tool path and mirror it for an opposite component. there will be several more instances this will come of value.

If you proceed with further assembly this is an easy ( at least geometrically ) correction. Cutting/ drawing a square or rectangle as large as you can, simply measure the diagonals and correct. Sorry if I am stating the obvious on the geometry.

again, Nice job,

Phill Pittman
www.masterwerkes.com
digicarve@verizon.net

[xairflyer]

Looking good, can't wait till I am running a dial indicator on mine !!