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CNC router 'OTOCOUP'
- Specifications -

On plans

My personal machine




Specifications of machine as on plans

Total width 3.20 m, range 2.60 m

Height 2.00 m, range 1.60 m

Depth range 90 mm

Router : prefer Kress FM6990 E (in Europe)

I beam weight : 10 kg

Carriage weight without router : 4 kg

Main beam (vertical) and horizontals beam made with mason ruler 100 x 18 x 1

Roller bearings, ABEC1

HTD type timing belts carrying

Specifications of my personal machine

Width 3.20 m, range 2.60 m

Height 2.10 m, range 1.60 m

Router Black et Decker 1300W, speed 8000-28000 trs/min, 3.5 kg

I beam weight : 10 kg

Carraiage weight with router : 7.5 kg

Depth range 90 mm

Carrying with Dyneema cables

Gear on motor 20 teeth, flywheel 60 dents

Carrying with Dyneema cables on 8mm diameter screw.

Theorically, we can get a load of 48 kg (motor torque 6.2 kg.cm), but the speed will not be that fast.

Dyneema cable rupture load is 70kg each (these kite cables are doubled to improve safety and stiffness).
For stiffness and time stability reasons, it might have been better to install steel cable diameter 0.6 mm (rupture load 24 kg). Dyneema is also prone to wearing.

It might have been better for simplicity and stiffness to do a carrying with timing belt, i feel this cable to be insufficiently stiff










Driller Dremel or Proxxon

Small jobs, a bit light for such a machine

100 W

8000 -28000 trs/min

500 g

70 à 100 Euros


3.2 mm

Router Black & Decker KW850E

Big jobs

1300 W

8000 -28000 trs/min

3.5 kg

80 Euros

6,6.35 et 8 mm

Router head from 600 to 800 W Bosch

Big jobs

600 à 800 W

20 000 trs/min

Est. 2 kg

Est. 150 Euros


Kress FM 6990 E

Machine used by professionals

900 W

8000 -26000 trs/min

1.6 kg

150 Euros


8 mm

In the US, you can find Porter Cable, or Bosch routers
As far as i know, Porter Cable cannot be found in Europe.
While american machines (Europe have other product lines), the Bosch routers seen on the listed Internet site can be found in Europe, by ordering it to local resellers.
The listed Black & Decker machine is an English machine, and i don't know if it can be found in the US. It's a bit heavy for a CNC job, but it's low cost, and for manual use, very ergonomic. It's weaker point is its pinch system ('high angle').


My machine is carried by cables but i think this is a wrong solution.

Plans are here studied for timing belts, with geared first stage.
Another option is now proposed with rack and pinion.

I recommend belts HTD 5M or AT5 from Gates in width 15 ou 25 mm. they are five to ten times stronger than 9.5 mm XL belts you can find everywhere, for a price nearly doubled. No doubts when choosing.

Bearings are roller bearings 608ZZ (diameter 8 x 22 x W 7). I paid them (ABEC1) 6 Euros (six !) for 16 bearings…

These bearings are protected, greased for life, but not tight. It is very important to not use oil on your machine, which will dissolve the grease, and your bearings will work dry.

I feel these bearing quality sufficient for the use. It is impossible to find industrial bearings at a lower cost.

Carrying motors

These steppers must be big torque, and herebelow are that i've selected :

. bipolar stepper Astrosyn 23LM -C355-P4 2.6V, 2A /phase torque 6.2kg/cm (86 oz.inch) (made in Thailand)

They costs 10 Euros each

They are in NEMA23 size (57 x 57, shaft diameter 6.35).

On Astrosyn stepper, back of the shaft is accessible, which allows to force in place gear in pushing on shaft instead of bearings.

These steppers have advantage of very low voltage, which allow to supply them in 12V with a chopper driver. Such power supplies (13.8 V) can be found at low price, because they are designed to supply equipment normally installed on car battery. They are not costly laboratory equipment.

To get more powerful steppers, go directly to manufacturers or resellers.

In Europe, you can try Nc-step (Germany) or www.ronchinimassimo.com/motori_passo_passo.htm (in Italian !)
Radiospares sells powerful steppers, at Radiospares prices...
A large choice with good prices is Nanotec

You can try at MAE (Italy), or else, salvage from photocopy machines.

In our domain, we will use two stepper size :
Dimensions are for fixation only, body length being highly variable.
- Nema 23 Squared axis to axis 47.6 mm - screw M5
  centering diameter : 38.1 mm - shaft diam 6.35 mm
  diameter stepper body : 56 mm
- Nema 34 Squared axis to axis : 70 mm - screw M5
  centering diameter : 73 mm - Shaft diam 9.525 mm
  diameter stepper body : 85 mm
Shaft length is not alawys constant.
'Short' Nema23 steppers weight from 500 to 700 grams

Steppers (Unipolar steppers can be installed with bipolar boards, but not the reverse, see here)
8 wires steppers can be wire either as unipolar or as bipolar steppers. data for 8 wires are given for parallel coils wiring.
Note : 1kg.cm = 0.87 Pound.Inch

NEMA Size Type torque
Model Price and supplier
23 Unip. 4.1V, 1.1A 3 SANYO StepSyn 10 Euros
23 Bip. 2.6V, 2A 6.1 ASTROSYN, SOYO 10 Euros -Remarkable perf/cost ratio
23 Unip. 6.6 V, 1.2A 6 TECO L0638 38 Euros at NC-step
23 Unip 5.4V, 1.4A 8.8 4H5618L03 79 Euros at Radiospares
23 Unip. 5.1V, 1.6A 10.5 TECO L2108 49.5 Euros at NC-step
23 Unip. 3.6V, 2A 11.25 Vexta PK266-E2.0B 98 Euros at NC-step
23 8 wires, 6V, 1.8 A 12 4H5618C03 85 Euros at Radiospares
23 8 wires, 1.96V, 2.8A 13 23SM056-028-8W-F-1.3 30 Euros at Stappenmotor
23 Bip. 2.1 A 9.25 MAE ? HS660020 ? at Massimo Ronchini
23 Unip 3A, Bip. 2.2A 11 MAE ? H7123-0740 ? at Massimo Ronchini
23 Unip 3A, Bip. 2.2A 16.5 MAE ? H7126-0740 ? at Massimo Ronchini
23 Unip. 4.5V, 2A 17.5 Vexta PK268-E2.0B-C3 95 Euros at NC-step
23 8 wires, 3.2V, 2.8A 17 23SM080-28-8W-F-1.7 40 Euros at Stappenmotor
23 8 wires, 2.3V, 3A 25 23SM112-030-8W-S-2.5 70 Euros at Stappenmotor
34 Unip. 3V, 2A 12 TECO 4H5618S1028 105 Euros at Radiospares
34 Unip 2.5V, 4.5A 22 TECO 4H5618S0428 125 Euros at Radiospares
34 8 wires, ?, 6.4 A 28 Nanotec ST8718S4508 -Wt 1.75 kg 125 Euros at Nanotec - Good
34 Bip. 6A 30 MAE ? 8221-6241 ? at Massimo Ronchini
34 Unip. 3.2V, 4.3 A 38 4800 250 Euros at Radiospares
34 8 wires, 1V, 6.4A 64 34SM114-064-8W-6.4 90 Euros at Stappenmotor

Some precisions about steppers reselled by Radiospares.
'Standards' steppers have not a very good speed potential and depending the model, their maximum speed cannot exceed 3.5 to 5 rotations/second. Their torque, if driven by a chopper at voltage 36V, remains fairly constant on the whole speed range.
High performance steppers (HSX), do have a speed ability from 30 to 40 rotations per second, depending the model.
Torque decrease regularly with speed, but for some steppers remains fairly good.
For example, stepper 23-HSX-206, supplied with 70V, still maintain a torque of 4 kg.cm at 30 rotation per second (1800 rpm), say 60% of nominal torque !
It's consumption is 4A, which is high. Such stepper can be driven by board Geckodrive (80V, 7A).
If you use a important gear ratio, this stepper can give an exceptionnal power for it's weight of 700 grams.
For more reasonnable use, stepper 23-HSX-202, same size, supplied in 36V, 1.4A/phase, bipolar, still have a torque of 4.5 kg.cm at 7.5 rotations per second. Torque drops over that speed.
And, for something largely exceeding amateur use, a stepper 34-HSX-312, weighting 3.6 kg, still give a torque of 20 kg.cm at 25 rotations per second, but requires a supply of 120V and a current of 9 A/phase (wired bipolar). and costs 251 Euros.

So, not all steppers are born equal... And if you go for performance, it might be useful to have a look on datasheets.

When you are running for high torque steppers, you will have to make a choice :
. A high current stepper, with a good ability for high speed.
. Lower current, but limited ability for speed.
This is simple, at given torque, to decrease the current, you will have to increase the wire turns in each coil. So, that increase the inductance of the stepper, and limit its speed ability.
It means that if you want high torque and high speed, you must use high current driver, as the Geckodrive cited hereabove.

And for ease of understanding :
1 kg = 9.81 N, which we will round to 10 N that gives :
1 kg.cm = 10 N.cm = 100 mN.m
moreover, as 1 ounce (oz) = 28.35 g
1 kg.cm = 13.89 oz.inch or else 1 oz.inch = 7.2 mN.m