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:

1. Glue and screw all joints
2. Make two side assemblies as shown in the first picture.
3. Add the four cross members to one of the side assemblies, picture 2.
4. With the base upside down use a doweling jig to drill 7/16 holes in the leg bases, picture 3.
5. Screw threaded inserts ( McMaster 92105A415, 5/16-18) in leg bases.
6. Add levelers (McMaster 23015T62)
7. 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.

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:

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

SLA7062/67 Step Motor Driver

The SLA7062/67 chip is a unipolar driver and can provide up to 3amps. The chip is hard to find and will cost about $10. each. Using Google, I found the three that I needed for my prototypes. Newark (Farnell) sells them but has no stock. The pcb's can be purchased from Batchpcb and below find the BOM and the circuit diagram. This board uses the 10 pin IDC connector (PMinMO) and is compatible with the CNC USB Motion Controller.

http://www.batchpcb.com/index.php/Products/58126

Bill of Material for C:\PCB PIC\SLAgm_02D.PCB
On 4/10/11 at 10:20:11 PM
Count	Label-Value	Pattern	Designation(s)	Mouser #
1	470uf 50v	C+400D200	C1	647-UHE1H471MPD
1	47uf 25v	C+200D80H31	C2	647-UHE1E470MDD
1	.1uf 100V	cap100	C3	80-C320C104K1R
1	56uf 50v	C+250D100H31	C4	647-UHE1H560MED
2	.1uf	cap100	C5 C6	80-C320C104K1R
1	FR202	DIODE0.35	D1	583-FR202-B
1	Dip Sw 2	DIP4	DS1	106-1202-EV
2	Fuse Holder	Fuse3517	F1	534-3517
1	IDC10-S	XIDC10	J1	517-D2510-6002-AR
1	SHeader 3	SIP3	JP1	517-647-01-03
1	LED Green	LED	LD1	638-HLMP1790
2	120R 1/8W 1%	AXIAL0.25	R1 R12	270-120-RC
2	2K2 1/8W 1%	AXIAL0.25	R10 R9	270-2.2K-RC
2	1K 1/8W	AXIAL0.25	R11 R8	299-1K-RC
6	See Text	AXIAL0.5L	R1A R1B R2A R2B R3A R3B	281-0.5-RC
3	220R 1/8W	AXIAL0.25	R2 R3 R4	299-220-RC
1	240R 1/8W 1%	AXIAL0.25	R5	270-240-RC
1	720R 1/8W 1%	AXIAL0.25	R6	270-720-RC
1	1K5 1/8W	AXIAL0.25	R7	299-1.5K-RC
1	4600X-1LF-3.3K	SIP6	RN1	652-4606X-1LF-3.3K
2	BC327	TO-92A	T1 T2	512-BC32740BU
1	STB-5.08 2	TB508A_2	TB1	538-39880-0402
2	STB-5.08 3	TB508-3	TB2 TB3	538-39880-0403
1	500R	TRIM2	TR1	652-3296W-1-500LF
1	SLA7062/67	SLA7062	U1	See Text
1	6N137	DIP8	U2	512-6N137
1	HCPL2630/31	DIP8	U3	512-HCPL-2630
1	LM317 (HV)	TO-220V	U4	LM317HVT Digikey
2	IC Socket 8pin		U2S U3S	517-4808-3004-CP