[TheMadHatter]

Good Day! I sincerely hope everyone is well.
Let's get right to it. I have purchased 2 cnc machines over the past couple years and have been unhappy with both. One was strictly a router machine without adjustable spindle speed and the other had a small work area. To be transparent I want to work with acrylic and some small aluminum pieces. After pricing some non Amazon machines and determining the ideal machines were out of my budget, I decided to DIY the build and oversize my current need of a 24" X 24" workable space to leave room for expansion and larger wood projects. I designed a machine made with steel with the intention of a large work area and stiff gantry. The proposed workable are is 4' X 4'
The gantry is made of 3" X 3" square tubing ( 2 pieces spaced 2.5" apart vertically ) professionally welded to 1/4" plate cut for risers. The base footprint of the machine is a 5' X 6' frame rectangle made from the same type 3" square tubing mentioned previously. Mounted to the gantry are HGR20 guide rails and HGH20CA blocks driven by an SFU1605 ballscrew. I also used these guide rails, blocks and ballscrew for the Y axis. I have a preassembled unit (Rattmotor ZBX100-200mm stroke) for the Z axis. I have nema 23, 425 oz/in, steppers on each axis. These are controlled by the DM542T drivers and a Mach3 6 axis controller. The spindle is a 230V VFD controlled 2.2KW water cooled unit up to 24000 rpm.

I have some concerns
The gantry is still at the machine shop so I cannot weigh it physically. With the limited information I have provided will I need a second Y travel ballscrew? I have an extra stepper and driver on hand in case this was a need.
Is the z axis assembly i purchased up to the task of holding this 80mm spindle? I replaced the smaller nema 23 with one mentioned before yet after attaching the spindle mount it seems small.

[pippin88]

Helpful if you post design pictures
And links to products

4 foot long gantry should be driven at both ends (two ball screws). Centre drive will result in a lot of racking when cutting near either end of the gantry

[TheMadHatter]

Spindle https://www.amazon.com/dp/B073TRP92V...t_details&th=1
Z axis https://www.amazon.com/dp/B09NMYYFTC...t_details&th=1
1500mm Rails https://www.ebay.com/itm/166134727967?var=465660294569
Stepper kit https://www.ebay.com/itm/334533596538?var=543595038200

Frame and Gantry attachment pdf

[hanermo]

A 4 foot gantry driven centrally is fine.
Endless VMC do this with much larger pieces cutting steel.

You should upsize your frame and gantry rigidity about 10x.

Easiest way imo, ime, is to epoxy secondary steel members to the current structure.
Mix cast iron powder into the epoxy, then glue the secondary pieces in.
You want about 6x10" box strusses for 5x6 foot frame.

The great thing about an epoxy joint is that you wont bend the alignments.
And yes, they bend with very little pressure, force.

[peteeng]

Hi TMH - The columns in your drawing are way too thin. It will wobble sideways when cutting in the X dirn. For the Y dirn one central or 2 side drives will work. If central everything has to be very stiff. Peter

[TheMadHatter]

Hi and thanks for the input. I have updated the drawing to reflect a missing piece. I have yet to determine what that section will be. Currently I am considering a section of 1/2" aluminum plate at 6" X 5' cut down to fit. This should add to the rigidity and maximize the z axis travel to the workable area. I considered a piece of 1/4" steel but I am on the fence. The gantry risers are cut from 1/4" steel plate.

[peteeng]

Hi TMH - 1/4" steel risers (commonly called columns) are not stiff enough transverse to the machine. They will need transverse webbing or use 1/2" or thicker to try match the stiffness of the gantry. Look at a 2"x3" section would be about right or since you have the 3x3 use it.... . Most people underestimate how stiff the column has to be... If you use ballscrews you can put 100's of kgf force sideways & you can flex a piece of 1/4" steel in your hands in a vice...Peter