I have been off on other workshop projects for several months, but I am now ready to get back to the CNC Router.
I have been investigating a torsion box assembly bench for general use in my shop. A torsion box provides a stable flat surface on which to assemble projects and furniture. Here are some links:
http://www.finewoodworking.com/PlansAndProjects/PlansAndProjectsArticle.aspx?id=28855
http://www.woodworkinghistory.com/glossary_torsion_box.htm
http://www.scottmorton.com/series/torsion-box-assembly-table/
http://www.google.com/search?q=torsion+box&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&ie=UTF-8&source=og&sa=N&hl=en&tab=wi&biw=1256&bih=862&tbm=isch#q=torsion+box&um=1&hl=en&client=firefox-a&sa=N&rls=org.mozilla:en-US:official&tbm=isch&fp=1&biw=1152&bih=702&cad=b&bav=on.2,or.r_gc.r_pw.,cf.osb
This last is a google image search of torsion boxes and includes some designed for CNC routers.
While I was investigating, I looked closely at the CNC router table surface that had already been built and found that it was no longer flat. The table surface is an integral part of our CNC router design providing flatness, rigidity and mass. For these reasons the table surface will be replaced by a 32" x 24" x 2.5" torsion box.
What is a torsion box? If you build a box with 6" sides, like a sand box and glue plywood skins, top and bottom, you have a torsion box. Placing the box between two saw horses and a load at the center, the top skin will try to compress and bottom stretch. As long as the spacing between sheets is held fixed the box will resist bending and its strength goes as the cube of the thickness. So we need to build a box with a grid of spacers inside, a honey comb to maintain constant thickness.
Building a torsion box is a chicken and egg problem. For the torsion box to be flat it must be built on a flat surface. So to build a flat surface you must first make a flat surface. Look at the first two links above and you can see how they solved that problem. Things are simpler for us since the surface is small; therefore, instead of jointing and planing 2x4's, I obtained three inexpensive 4ft levels from Harbor Freight for $7 each. These levels will take the place of the 2x4's and eliminate the need for a jointer and planer which I don't have.
Our torsion box will be built from MDF with the sides and core using 1/2" material and the skins 1/4" sheet.
Sunday, December 25, 2011
Tuesday, May 24, 2011
StepTB6560 Step Motor Driver
Schematic
BOM: To be added.
Batchpcb:
http://www.batchpcb.com/product_info.php?products_id=50084&check=33e8b36118a8e7ceaf3179ebcbc71752
Step298 Step Motor Driver
Schematic:
BOM:
Bill of Material for Step298_04C.PCB | ||||
On 5/27/11 at 9:25:51 AM | ||||
Qty | Label-Value | Pattern | Designation(s) | Mouser |
9 | FR202 | DIODE0.4 | D1 D2 D3 D4 D5 D6 D7 D8 D9 | 583-FR202-B |
1 | 220pf | cap100s | C1 | 80-C315C221J1G |
5 | .1uf | cap100s | C10 C4 C6 C7 C9 | 80-C320C104K1R |
1 | 3300pf | cap100s | C2 | 80-C320C332J1G |
1 | .1uf 100v | cap100s | C3 | 80-C320C104K1R |
1 | 10nf | cap100s | C5 | 581-SR151C103K |
1 | 220uf 63VDC | C+400D200 | C8 | 647-UHE1J221MPD |
2 | Fuseholder | Fuse3517 | F1 | 534-3517 |
1 | Heatsink | HS677A | HS1 | 677-20ABP |
1 | 66506-001LF | XIDC10 | J1 | 517-D2510-6002-AR |
1 | SIP3 | JP1 | 517-647-01-03 | |
3 | SIP2 | JP2 JP3 TP1 | 517-647-01-02 | |
1 | LED | LD1 | 638-HLMP1790 | |
4 | 1R 1W | AXIAL0.5L | R1 R2 R3 R4 | 282-1.0-RC |
3 | 10K | AXIAL0.3 | R10 R11 R9 | 299-10K-RC |
1 | 22K | AXIAL0.3 | R12 | 299-22K-RC |
1 | 1K | AXIAL0.3 | R13 | 299-1k-RC |
1 | 240R 1% | AXIAL0.25 | R15 | 270-240-RC |
1 | 715R 1% | AXIAL0.25 | R16 | 270-715-RC |
4 | 330R | AXIAL0.25 | R17 R18 R19 R21 | 299-330-RC |
3 | 1K | AXIAL0.25 | R20 R22 R23 | 299-1K-RC |
1 | 1K5 | AXIAL0.25 | R24 | 299-1.5K-RC |
2 | 2K 1% | AXIAL0.3 | R6 R7 | 270-2K-RC |
1 | 2K | AXIAL0.3 | R8 | 299-2K-RC |
1 | 2N3904 | TO-92A | T1 | 512-2N3904BU |
3 | T-Block-2 | MKD2X | TB1 TB2 TB3 | 538-39880-0402 |
1 | 2K | TRIM2 | TR1 | 858-67WR1KLF |
1 | L298N | L298 | U1 | |
1 | L297 | DIP20 | U2 | |
1 | 6N137 | DIP8 | U3 | 512-6N137 |
1 | HCPL2630 | DIP8 | U4 | 512-HCPL-2630/31 |
1 | LM317HV | TO-220V | U5 | LM317HVT Digikey |
1 | IC Socket 20p | U2S | 517-4820-3004-CP | |
2 | IC Socket 8p | U3S,U4S | 517-4808-3004-CP | |
Batchpcb:
http://www.batchpcb.com/product_info.php?products_id=46128&check=d1866a6ff4033116953019e09b4f316c
Sunday, April 24, 2011
Table for CNC Router
I decided that I needed a table on which to both assemble and run the CNC router and which incorporates a heavy stable top made of MDF. The table design is based on Scott's router table shown on this site, http://www.scottmoore.net/projects/router/index.html. The construction uses Kreg pocket screws and glued joints and is made of Poplar. Adjustable feet are incorporated for leveling the table and, possibly, retractable casters. Since Scott's site shows construction details, only a few photos will be shown for this project with an explanation of any differences.
The table height is 37 1/2" with a top surface 24" by 32" by 1 1/2". The home stores carry 1 1/2" square Poplar cut to 36" which was used for the legs. The top is made from two pieces of MDF glued together with wood glue. A trowel was used to spread the glue in a thin layer and clamps and heavy weights used during bonding.
The construction sequence is as follows:
Poplar is soft enough that care must be taken using Kreg screws, so set the torque on the drill to prevent screw tear-out.
The table height is 37 1/2" with a top surface 24" by 32" by 1 1/2". The home stores carry 1 1/2" square Poplar cut to 36" which was used for the legs. The top is made from two pieces of MDF glued together with wood glue. A trowel was used to spread the glue in a thin layer and clamps and heavy weights used during bonding.
The construction sequence is as follows:
- Glue and screw all joints
- Make two side assemblies as shown in the first picture.
- Add the four cross members to one of the side assemblies, picture 2.
- With the base upside down use a doweling jig to drill 7/16 holes in the leg bases, picture 3.
- Screw threaded inserts ( McMaster 92105A415, 5/16-18) in leg bases.
- Add levelers (McMaster 23015T62)
- Turn base right side up and attach top. Note pocket screw holes in first picture for this purpose.
Poplar is soft enough that care must be taken using Kreg screws, so set the torque on the drill to prevent screw tear-out.
 |
| Side Assembly |
 |
| Adding side pieces |
 |
| Drilling holes for 5/16 threaded insert for levelers using Harbor Freight doweling jig. |
 |
| Assembled table |
 |
| Table with CNC Router base end pieces. |
Wednesday, April 20, 2011
SLA7078 Step Motor Driver
A step motor driver using the SLA7078MPR has several advantages over one using the SLA7062M: one, a newer design, two,seems to be more available with a price of $12ea or $8 per ten, three, SLA7078 series has built in sense resistors and,four, the PR version has built in protection circuits.
The design shown below has two version: with and without opto isolation. An idle delay feature has been incorporated which places the motor in half power mode when idle for 10 seconds. This driver does not set motor current by a selection of sense resistors as with the SLA7062 driver. With that driver the reference voltage was fixed, such that a .5 ohm resistor gave 1 amp motor current, so three .5 ohm resistors in parallel gave 3 amps. In the SLA7078 the sense resistors are located in the chip and current settings are adjusted using the trimmer pot. To set the current, a multimeter is attached to the reference signal, JC1 in schematic above, and the trimmer adjusted to a voltage given in the SLA7078 datasheet.
The delay feature uses a 74HCT4538 retriggerable oneshot. A circuit using a LMC555 was investigated which would probably work, but the board space required is about the same as with the 4538 even though only half the 4538 package is used. The circuit works as follows: as long as step signals are arriving, the oneshot stays triggered and the motor stays at full power, but when the step pulses stop, 10 seconds later the motor switches to half power. The first step after a delay should immediately switch the motor to full power. Whether this switching is fast enough will be determined during testing of the prototype driver.
Stepit 4A: Driver using SLA7078MPR with delay
Schematic:
BOM:
Next will be the schematic and BOM for the opto-isolated version, Stepit 4
Stepit 4: Driver using SLA7078MPR with opto-isolation, regulator and delay
Schematic:
BOM:
The design shown below has two version: with and without opto isolation. An idle delay feature has been incorporated which places the motor in half power mode when idle for 10 seconds. This driver does not set motor current by a selection of sense resistors as with the SLA7062 driver. With that driver the reference voltage was fixed, such that a .5 ohm resistor gave 1 amp motor current, so three .5 ohm resistors in parallel gave 3 amps. In the SLA7078 the sense resistors are located in the chip and current settings are adjusted using the trimmer pot. To set the current, a multimeter is attached to the reference signal, JC1 in schematic above, and the trimmer adjusted to a voltage given in the SLA7078 datasheet.
The delay feature uses a 74HCT4538 retriggerable oneshot. A circuit using a LMC555 was investigated which would probably work, but the board space required is about the same as with the 4538 even though only half the 4538 package is used. The circuit works as follows: as long as step signals are arriving, the oneshot stays triggered and the motor stays at full power, but when the step pulses stop, 10 seconds later the motor switches to half power. The first step after a delay should immediately switch the motor to full power. Whether this switching is fast enough will be determined during testing of the prototype driver.
Stepit 4A: Driver using SLA7078MPR with delay
Schematic:
BOM:
Bill of Material for C:\PCB PIC\SLAgm_04C.PCB | ||||
On 4/28/11 at 12:18:18 AM | ||||
Count | Label-Value | Pattern | Designation(s) | Mouser |
1 | 330uf 50V | C+400D200 | C1 | 647-UHE1H331MPD |
1 | 47uf | C+200D80H31 | C2 | 647-UHE1E470MDD |
4 | .1uf | cap100 | C3 C4 C5 C7 | 80-C320C104K1R |
1 | 47uf 50V | C+200D100H31 | C6 | 647-UPW1E470MDD |
1 | 15uf tant | cap100 | C8 | 581-TAP156K016SCS |
1 | DIP6 | DS1 | 774-2063ST | |
1 | XIDC10 | J1 | 517-D2510-6002-AR | |
2 | SIP2 | JC1 JP1 | 517-647-01-02 | |
1 | SIP3 | JP2 | 517-647-01-03 | |
4 | 10K | AXIAL0.25 | R1 R5 R6 R8 | 299-10K-RC |
1 | 4k7 | AXIAL0.25 | R2 | 299-4.7k-RC |
1 | 1M | AXIAL0.25 | R3 | 299-1M-RC |
3 | 1K | AXIAL0.25 | R4 R7 R9 | 299-1K-RC |
1 | 10K | SIP8 | RN1 | 265-10K-RC |
2 | BC327 | TO-92A | T1 T2 | 512-BC32740BU |
1 | BC547 | TO-92A | T3 | 512-BC547CBU |
1 | TB508A_2 | TB1 | 538-39880-0402 | |
2 | TB508-3 | TB2 TB3 | 538-39880-0403 | |
1 | 1K | TRIM2 | TR1 | 858-67WR1KLF |
1 | SLA7078MPR | SLA7078 | U1 | |
1 | 74HCT4538 | DIP16 | U2 | 595-CD74HCT4538E |
1 | DIP16 Socket | 517-4816-3004-CP | ||
Next will be the schematic and BOM for the opto-isolated version, Stepit 4
Stepit 4: Driver using SLA7078MPR with opto-isolation, regulator and delay
Schematic:
BOM:
Bill of Material for C:\PCB PIC\SLAgm_05A.PCB | ||||
On 4/30/11 at 2:23:09 PM | ||||
Count | Label-Value | Pattern | Designation(s) | Mouser |
1 | 330uf 50V | C+400D200 | C1 | 647-UHE1H331MPD |
6 | .1uf | cap100 | C10 C4 C5 C6 C8 C9 | 80-C320C104K1R |
1 | 47uf | C+200D80H31 | C2 | 647-UHE1E470MDD |
1 | 47uf 50V | C+200D100H31 | C3 | 647-UPW1E470MDD |
1 | 15uf | cap100 | C7 | 581-TAP156K016SCS |
1 | FR202 | DIODE0.35 | D1 | 583-FR202-B |
1 | DIP6 | DS1 | 774-2063ST | |
2 | Fuse Holder | Fuse3517 | F1 | 534-3517 |
1 | Socket IDC 10p | XIDC10 | J1 | 517-D2510-6002-AR |
2 | SIP2 | JC1 JP1 | 517-647-01-02 | |
1 | SIP3 | JP2 | 517-647-01-03 | |
1 | HLMP1790 | LED | LD1 | 638-HLMP1790 |
1 | 240R 1% | AXIAL0.25 | R1 | 270-240-RC |
1 | 1M | AXIAL0.25 | R10 | 299-1M-RC |
5 | 1K | AXIAL0.25 | R11 R12 R6 R7 R9 | 299-1K-RC |
4 | 10K | AXIAL0.25 | R13 R14 R15 R16 | 299-10K-RC |
1 | 720R 1% | AXIAL0.25 | R2 | 270-720-RC |
3 | 330R | AXIAL0.25 | R3 R4 R5 | 299-330-RC |
1 | 4K7 | AXIAL0.25 | R8 | 299-4.7K-RC |
1 | 10K | SIP8 | RN1 | 265-10K-RC |
2 | BC327 | TO-92A | T1 T2 | 512-BC32740BU |
1 | BC547 | TO-92A | T3 | 512-BC547CBU |
1 | TB508A_2 | TB1 | 538-39880-0402 | |
2 | TB508-3 | TB2 TB3 | 538-39880-0403 | |
1 | 1K | TRIM2 | TR1 | 858-67WR1KLF |
1 | SLA7078MPR | SLA7078 | U1 | |
1 | 74HCT4538 | DIP16 | U2 | 595-CD74HCT4538E |
1 | 6N137 | DIP8 | U3 | 512-6N137 |
1 | HCPL2631 | DIP8 | U4 | 512-HCPL-2630/31 |
1 | LM317HV | TO-220V | U5 | LM317HVT Digikey |
2 | IC Socket 8p | U3S U4S | 517-4808-3004-CP | |
1 | IC Socket 16p | U2S | 517-4816-3004-CP | |
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