# CNC Machine - for home-building aircraft

Discussion in 'Workshop Tips and Secrets / Tools' started by Rienk, Apr 17, 2015.

### Help Support HomeBuiltAirplanes Forum by donating:

1. Apr 17, 2015

### Rienk

#### Well-Known Member

Joined:
Oct 11, 2008
Messages:
1,364
190
Location:
Santa Maria, CA (SMX)
This is a spin-off of Fritz's 'VP-21 HWC' thread, where we were discussing the possibility of more homebuilders being able to have their own CNC machine, and providing "open-source" plans, instructions, and parts lists (with suppliers) in order for people to quickly and inexpensively build one.
Kind of like the "90 Day Wonder" airplane, but instead a "40 Hour Wonder". (Fritz prefers days, but I started the thread, and I prefer hours... ).

The current goal is to be able to build it in less than 40 hours of work (including specialty stuff), and for less than 3,000 (including router/spindle, everything to hook up to a computer and be able to run; tooling extra). The ideal machine would: • Be able to, one way or the other, handle full 4'x8' sheets. • Be able to cut up to 1" sheet goods, and at least 1/8" aluminum. • Have side rails that are below the work surface, so that the table can also be used as a workbench. • Run off of 110v power (even if needing two circuits). • Have vacuum hold down capability. • Have vacuum collection. • Use OTS parts and supplies. • Use OTS software and controls (including free-ware). . Here are a few 'wish list' items. • Have room for a rotary 4th axis on the side (would make the Y axis gantry 5' wide?) • Use a water-cooled spindle instead of a router. . A small sponsorship is available to help offset the cost of putting together such a package (especially fabrication and assembly photos/videos/animations). Once the design is set, others are welcome to put together packages, kits, whatever, to make available to those who don't have certain capabilities or want to save time. I'm curious to see if such a project will get legs and take off - I sure hope so! FritzW likes this. 2. Apr 17, 2015 ### Jay Kempf ### Jay Kempf #### Well-Known MemberLifetime Supporter Joined: Apr 13, 2009 Messages: 3,662 Likes Received: 929 Location: Warren, VT USA There are a few things in your list that are going to drive the cost up significantly. The water cooled spindle. Any linear axis past 6', 110 power can work OK for all but high powered spindles. The spindle, speed and strength, collet are a whole world unto themselves. I built a custom spindle to start. Side rails below the work surface can be worked around with a bench top that goes on top of the rails. Making a stowable gantry so that it is way out of the way so you have three sides of bench available to you is a more reasonable compromise. For a 4th axis you can have a manual rotisserie with pins every say 90 degrees. You run a program and program in a stop. You turn the part and start the program again. That way you can reach and make anything that looks like a 5 axis part with 3 axis. Just takes some clever CAD/CAM trickery. Not hard, just out of the box. My machine looks like this... You could have a fold up front and rear table to get a 4x8 bench. I made everything in my shop on casters so I can reconfigure the shop and stow things when not in use. #### Attached Files: • ###### cnc persp 24 apr 12.jpg File size: 23.2 KB Views: 369 Last edited by a moderator: May 26, 2015 3. Apr 17, 2015 ### pictsidhe ### pictsidhe #### Well-Known Member Joined: Jul 15, 2014 Messages: 6,835 Likes Received: 1,832 Location: North Carolina 40 hours for everything is going to be tricky, particularly if you want to keep the cost down. I've made some very flat and solid 8x4 benches, but they need to be made carefully, which slows things down a lot compared to a flatish but fast one. although with this, you could use itself to route its own bed flat! A double layer of 3/4ish ply makes a superb workbench. You could route vacuum channels in the bottom, glue or screw the top on, then drill the top layer. Again, you could use itself to do that. 4. Apr 17, 2015 ### FritzW ### FritzW #### Well-Known Member Joined: Jan 31, 2011 Messages: 3,627 Likes Received: 3,251 Location: Las Cruces, NM ...just a couple of thoughts 1) Why would want to use a water cooled spindle? 2) I'm very interested in how you handle the vacuum hold down. I'd really like to have that capability on mine. 5. Apr 17, 2015 ### Hot Wings ### Hot Wings #### Well-Known MemberHBA Supporter Joined: Nov 14, 2009 Messages: 6,352 Likes Received: 2,282 Location: Rocky Mountains The one I ran had the bottom side sealed, and sloped to collect the fluid runoff. Over the basic support channels we used plain old peg board as a sacrificial layer and to transmit the vacuum to the work piece. To maintain the vacuum for small bits we had other sheets of Masonite in various sizes to block off the unused portions of the table. Sometimes if the project had a lot of little parts by the time it had cut around 70% of the 5x12 surface we had to toss on some more vacuum shields to keep the part from moving. It's not good enough for more than a basic router because there is no way to keep the Z axis tolerances under control with such crude methods, but for flat stock it was easy and fast. 6. Apr 17, 2015 ### ScaleBirdsScott ### ScaleBirdsScott #### Well-Known Member Joined: Feb 10, 2015 Messages: 1,033 Likes Received: 656 Location: Uncasville, CT I like the water cooled spindle on my machine: the price difference is marginal, and using a water cooling setup does a lot for noise and ensures the machine can stay cool on long runs (though I have yet to have a job last more than an hour, I have run the machine over multiple hours on different jobs in a marathon run. I've yet to see the spindle ever get above 80F) Running the coolant is an extra step, but it also is useful for, in my case, cooling the G540 which is known to get warm. I also like that it's closed and there's no chance of debris+fan causing issues. Not that I am an expert on air-cooled spindles and its probably not a major concern: I just know that MDF dust gets everywhere and a sealed, quiet spindle is comforting. The vac hold-down is going to add a lot to a homebuilt CNC project IMO. It is handy to have, but I'm not sure how well it will work with small parts (they tend to go flying on even commercial vac hold down machines) and the cost/complexity/noise again becomes a concern when doing a budget build. One can use tabs, to prevent smalls from going places, but at that point it's not THAT much more work to just use a few screws in pre-determined safe zones to hold down the work pieces. But yeah, Not impossible to have the vac, just something that either has to be built in from the beginning and is integral to the design, increasing the cost/complexity less; or something that is an added on 'bonus' feature down the road for extra cost and time when needed. Oh, and with a vac hold down, I would think now one needs to be running two vac systems on the machine: one for hold down and one for dust collection? And if both are shop-vac style units running on full blast, plus an air-cooled spindle or god forbid a wood router tool, its going to sound like the inside of a Tu-95 unless you have a fabled large workshop to use. As-is I've tried to keep all the noise-makers to the minimum but it's still not quiet when running wood. Noise-cancelling shooting earmuffs help, with the addition of some heavy metal from the aux input. The quietest is running aluinum, the spindle isn't loud on its own and it hardly makes noise when cutting, and no dust collection needed so the blowers and vacuums are all shut off. I can run the machine in that state with no earpro. 7. Apr 17, 2015 ### FritzW ### FritzW #### Well-Known Member Joined: Jan 31, 2011 Messages: 3,627 Likes Received: 3,251 Location: Las Cruces, NM This was my attempt at vacuum hold down for cutting aluminum gussets. I put a layer of silicone on the top about .010 thick to act as a seal before I cut the holes. It held great until a few holes got exposed so I chased behind the spindle with pieces of paper to seal the holes. Even then I was getting quite a few "whirling zingers of death". I ended havening to use hold down tabs. It might have worked on a larger scale but I think the gussets were just too small. 8. Apr 18, 2015 ### JamesG ### JamesG #### Well-Known Member Joined: Feb 10, 2011 Messages: 2,408 Likes Received: 754 Location: Columbus, GA and Albuquerque, NM Look into vacumn forming tables, they are cousins. The holes can/need to be smaller than you'd think. 9. Apr 18, 2015 ### JamesG ### JamesG #### Well-Known Member Joined: Feb 10, 2011 Messages: 2,408 Likes Received: 754 Location: Columbus, GA and Albuquerque, NM I have the typical 2 car garage that I have converted to 1 1/4 car garage to house my personal work shop. On thing I am considering/day dreaming about is building a large CNC router/cutter machine, but instead of the conventional bed and gantry system, its actually upside down, where the frame is actually more like a gantry crane in that the X and Y axis tracks are up at ceiling level and there is a suspended arm for the Z axis. When not in use (ie: when wife wants to park her fancy Subaru out of the weather) it can be stowed out of the way, but it can be brought back into action by simply setting up a MDF platform and aligning the work with witness marks in the floor and then zeroing the machine on where it happens to be. Someday, when I actually get the mess cleaned up... 10. Apr 18, 2015 ### BJC ### BJC #### Well-Known Member Joined: Oct 7, 2013 Messages: 9,512 Likes Received: 6,289 Location: 97FL, Florida, USA Unicycle? BJC 11. Apr 18, 2015 ### Rienk ### Rienk #### Well-Known Member Joined: Oct 11, 2008 Messages: 1,364 Likes Received: 190 Location: Santa Maria, CA (SMX) You can get 3hp (2.2kw) water or air cooled spindles (with controller) for200-300 these days. It would be nice if the kit allowed for either.

Vacuum table is pretty easy for sheet goods, but not for small parts.
For ours, we made a table top made out of several layers of MDF. We carved channels in one layer to make four separate zones (about 2'x4' each). Each one had a hole through the bottom, with PVC fittings glued in. These are connected to a manifold along one side of the table, each with a cheap PVC valve (and another valve to turn on/off all of them). This in turn is connected to our large rotary vane vacuum pump.
The layer with channels was then coated in resin to prevent airleaks.
We then removed the top and bottom 1/8" of an 1" MDF sheet (would prefer LDF). This is where the bulk of the glue is, in a sheet. Once it is removed, the sheet is incredibly porous - and makes a great sacraficial vacuum table top. We counter sink holes almost 1/2", and screw it down to the channeled sheet below it.
It holds down sheets really well. Though we do need to cover the bulk of any area (nor covered by the material being cut) with plastic sheeting, per zone. We don't particularly care if the bit hits this sheet occasionally, and we simply relevel the table every once in a while, until we get close to the level of the screws, and then start over. Even when we use the table every day, the vacuum sheet lasts for months. Unless you really screw up, one such sheet can last for 6-12 months.

But again, this only works for larger sheet material.
Everything else we simply screw down with drywall screws (sometimes we do both, just to keep anything from slipping.

Oh, another thing. We prefer not to use our "at the tool" vacuum to remove dust. We like to leave the dust in the cut path, as it does a good job of sealing the vacuum there, so vacuum is hardly ever diminished. We're going to be building a recirculating vacuum "wall", so that most everything is drawn to that. the return air will also loop around to the other side of the machine, and gently 'blow' back toward the wall... we'll see how it works!

12. Apr 18, 2015

### Rienk

#### Well-Known Member

Joined:
Oct 11, 2008
Messages:
1,364
190
Location:
Santa Maria, CA (SMX)
I really like the concept of the Shopbot Buddy, which is a portable 4'x2' CNC system most of the time, but can be quickly changed to handle larger sheets when needed. This lets someone keep it accessible in their shop, and roll it to the middle of the floor (or even into the driveway) to cut larger pieces, without dedicating a lot of space to it.(the picture below isn't great, but it should give the idea). On the other hand, a 4'x8' table that can have three open sides (no rails in the way of the bed), would make a great combo work table as well.My table saw is in the middle of a 9'x9' runoff table, which we always use as a work table - and often has to be cleaned off enough to actually use the saw, which can be a problem...

13. Apr 18, 2015

### JamesG

#### Well-Known Member

Joined:
Feb 10, 2011
Messages:
2,408
754
Location:
Columbus, GA and Albuquerque, NM
Theoretically motorcycles, but in reality... kids toys. :/

14. Apr 18, 2015

### pictsidhe

#### Well-Known Member

Joined:
Jul 15, 2014
Messages:
6,835
1,832
Location:
North Carolina
You can't have the wife's car and the kids toys in your man-cave. That's your refuge.
You need to lay down the law!

JamesG likes this.
15. Apr 18, 2015

### pictsidhe

#### Well-Known Member

Joined:
Jul 15, 2014
Messages:
6,835
1,832
Location:
North Carolina
I've used vacuum cleaners for hold down on a 8x4 foam cutter, they're rather inefficient. A centrifugal blower can work well. The holes don't need to be large.

16. Apr 18, 2015

### Aerowerx

#### Well-Known Member

Joined:
Dec 1, 2011
Messages:
4,975
1,354
Location:
Marion, Ohio
When the topic of CNC came up in Fritz's thread, I started looking around the WWW to see what it would take to build one.

One idea I came across was to mount the table on edge, to minimize floor space.

17. Apr 18, 2015

### FritzW

#### Well-Known Member

Joined:
Jan 31, 2011
Messages:
3,627
3,251
Location:
Las Cruces, NM
Maybe something like a Murphy bed or a tilt top table...

18. Apr 18, 2015

### ekimneirbo

#### Banned

Joined:
Oct 31, 2014
Messages:
1,009
324
Location:
Deep South
While I can see that it might be nice to be able to machine smaller parts with blended contours or something the size of an instrument panel, I am wondering why a builder might want something that would do 4 x 8 material. When doing small parts you can usually clamp the outside edge of the raw material, or drill holes thru somewhere in the part so you can screw it down. The holes are then eliminated when the machining is done. By that I mean, if someone were making an instrument panel, you would drill holes where the gages are going to be installed. When the hole for the gage is machined out, the hole in the center goes with it. Sometimes you have to use a combination of clamping methods as the machining proceeds. Holding a part down with a vacuum seems simple, but a sudden loss of vacuum can wreak havoc on the part and the machinist. Surface Grinding machines have magnetic tables. Of course that only works with steel parts. All the older machinists always worked to the right side of the shop.......cause if someone forgot to turn the magnet on before starting the grinding tables oscillation........all the parts came shooting off the table like a machine gun.....to the left. Holding a part securely when machining is very important and any loss of the force used to secure it is a very dangerous proposition. While CNC may seem like a neat thing to have, as the size of your components increases, so does your need for ridgidity in your machine tool.

19. Apr 19, 2015

### Rienk

#### Well-Known Member

Joined:
Oct 11, 2008
Messages:
1,364
190
Location:
Santa Maria, CA (SMX)
An interesting idea, except that the Z axis head is so tall, I think it would take up way too much wall space?

20. Apr 19, 2015

Joined:
Feb 10, 2011
Messages:
2,408