CNC_0001

MAKE: Workbench - X-axis - Assembly

Preliminary Considerations:

Length of Travel on X-axis:

Y-carriage + A-carriage = 473.2377mm. Offset of tracks might reduce the previous value by ??mm.

Rotor radius = 117" = 2,971.8mm.

Over-travel for limit switches and end wrapping beyond the end of the part = 6" =150mm

Total = 333mm + 2,971.8mm + 150mm = 3,455mm = 136". However, it can be up to 4,000mm, to fill the table length by buying 2,500mm rails.

The X-axis might be 8,000mm if there is intent to produce both opposing blades at the same time. See; DESIGN: UniCopter ~ Rotor - Hub - Twinned Blades

To achieve low and high travel speed.

Consider the use of two encoders. Use the one with a low pulse output when winding the spar. Or, can the quadratic be switched (20'/min x 4 = 80fpm.

Alternatively, consider two gears that are both in full time contact with the rack. One is associated with a larger gear and the other is associated with a small gear. The gear on the motor can be intermeshed with either the larger or the smaller.

Perhaps the high speed reduction should be around 18:1 and the slow speed reduction another 2:1 or 3:1; if the pinion has a 2"diameter ??

Minimum Possible Move Distance = 0.0001" = 0.00254 mm. ~ "This is the absolute limit to the accuracy of the work done on the Y-axis." ~ from Mack3Mill, section 4.5.2. I believe that this means that the 'steps per unit' is 10,000, with the unit being inches. ~ see; Mack3Mill, section 5.5.1.4.

Maximum Travel Speed = 132 fpm = 2.2 fps. = 0.670 meter/sec. For winding the spar.

Ref. The maximum X-axis travel speed of the McClean Anderson filament winders is 200 fpm.

Maximum Winding Speed (for spar) = 132 fpm = 0.670 meter/sec. Must include Gecko G901 to increase the step-rate from the servo controller to the motor. Don't think so. The increased count will be very near the motor's Continuous (no load) rpm.

Maximum Winding Speed (for torque tube) = 20 fpm = 4 ips = 100 mm/sec. This is currently a guess.

Maximum Jog Speed = 236 ipm = 100 mm/sec.. Should this be a little faster?

This may be the same as Maximum Travel Speed UNLESS the Maximum Travel Speed necessitates the use of the PLL step pules multiplier, because Mack3's 45,000 pulses per second is not fast enough. The use of the G901 (with a G320) may be better since the jumpers are easier to get at for electrical switching. The use of the very high steps per unit will mean that the Minimum Possible Move Distance is reduced when traveling near the Maximum Travel Speed. These notes may be wrong.

Maximum Cutting Speed = 120 ipm. = 50 mm/sec. Should this be a little faster? Perhaps 'head-room' comes from the speed between cutting and jogging?

Force = xx guesstamate N (newton), 25 guesstamate lbf (pound-force).

Acceleration: Note that faster the travel means greater acceleration and deceleration forces. Is there any reason for not having a slow acceleration and deceleration on the X-axis?

Give the X-axis sufficient strength and accuracy etc. so that it is compatible with the selected Y and Z-axii's linear actuators.

Must make sure that the table's frame is strong enough that force on the tracks will not deflect them, particularly in the center of the span where a diagonal brace may be difficult.

It has been mentioned on CNCzone that a 'sloppy' screw and low friction ball slided may result in the motor fighting to hold position. This might also be the case with rack & gear and the THK bearing blocks.

damae on CNCzone re milling forces;

"In my quest to figure out how much side-cutting force is typical of a router (and how much I'll need), I found a useful tidbit on Shopsabre's website.

Their big daddy machine, the 7414, has 150 lbf of cutting force and does 300-600 IPM (depending on motor option). That's a big machine with a 6' x 12' cutting area.

http://www.shopsabre.com/cnc-machin...router-7214.htm"

This is for spindles of 3 to 10 hp. Cutting speed of 300 IPM. (= 25fpm.) over 150 lbs of cutting force strong enough to cut the most demanding materials that the sign cabinet and fabrication industry of all types can offer."

Components:

Linear Rails and Blocks:

Going with 2 rails, 160mm, 3 blocks and overhang the Y-axis linear slide. Build the table for a approximately 12 ft of travel and add the additional rail at some time in the future.

BUY: Shop Equipment - CNC - Workstation - Linear Rails and Blocks ~ Item # 1471:

I am going with THK.

THK Technical Info: http://www.thk.com/technical/download/a.html#1 . I have printed most of this catalog. See front page in binder.

Have:

2 only SR25 rails approximately 1,600 mm long.

Still Required:

2 only SR25 rails approximately 1,960 mm long; for a total double track of just under 3,560 mm. (140") after machining the abutting ends.

Alternatively:

Consider using only one track, and have the static load fairly evenly balanced on both sides of the track.

The static permissible moment on a single block is 0.21 kN.m (88.5 lbf.ft). Two blocks will be 177 lbf.ft. The mid point of Y travel = 100 mm, plus 50 mm for half the z slide width, plus 37 mm for half the blocks width, means that the average arm length is 187 mm (7.36'). The maximum permissible static load is therefore (0.21 * 2) * (1000/187) = 2.246 kN = 505 pounds STATIC. The dynamic permissible moment will be less. The situation will be improved if the A-axis is located closer to this track.

If three blocks are used, and the alignments are perfect, then the permissible load can probably be increased by 1.5. The track and table will have to be approximately 7" longer to take the additional bearing block.

Counterbalance this moment by putting the X-axis motor, reducer and other items on the other side of the track.

If one or more operations exert more of a moment on the linear blocks then other operations do, consider having a spring-loaded cam running on a flat track. This cam would be used when the operations that are causing an unbalanced moment are being done. This spring-loaded force will compensate for a percentage of the unbalanced moment.

2 * 1600 = 3,200 mm = 125.98". After machining the abutting ends, leaving 83 + 83 = 166 mm for the two blocks and a 34 mm gap (for the grease nipple) the usable travel will be 3,200 - 200 = 3,000 mm = 118.1" = 9.84'. The current blade length (over the pins) is currently 114" [1443.dc] and there must be room for wrapping on both ends. If necessary, a short section of track could be inserted, or the table built to take this small section in the future, if needed and/or a short section of track becomes available.

The additional 3 bearing blocks could be used as replacement parts for the two that are to be used.

Motion Industries shows the following in stock; https://www.motionindustries.com/motion3/jsp/mi/motion.jsp

SR25+220LY Rail for $78.13 US (8.6")

SR25+280LY Rail for $91.47 US (11.0")

SR25+340LY Rail for $99.09 US (13.3")

SR25+460LY Rail for $120.06 US (18.1")

SR25+640LY Rail for $161.98 US (25.1")

~ and more ~

SR25+1600LY Rail for $388.75 US (62.9") Have 2

SR25+2500LY Rail for $657.45 US (98.4")

Codes following the length: 'L' stand for length. Next is the accuracy as noted on table 5 on page A-221. Next is the material; 'M' is stainless steel.'K' is the tap type symbol for the holes in the rail. God knows what 'Y' stands for. Maybe 'steel'????

It also looks like orders can also be placed directly with THK over the net; http://www.tos-world.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=10051&storeId=10001&categoryId=11919&langId=-1&topcategoryId=11901

The best prices for new could be Technico https://www.technico.com/technico/category.aspx?SID=1&Category_ID=62

______________________________

Calculations:

1 N = 0.2248 lbf

1 N.m = 1.5488 lbf.ft

	Basic Dynamic Load Rating	Basic Static Load Rating
	C	C_O
Radial Direction:	20.3 kN = 4,564 lbf	39.5 kN = 8,880 lbf
Reverse Radial Direction:	C_L = 0.62 * C = 12.59 kN = 2,830lbf	C_OL = 0.50 * C_O = 19.75 kN = 4,440 lbf
Lateral Directions:	C_T = 0.56 * C = 11.37 kN = 2,556 lbf	C_OT = 0.43 * C_O = 16.98 kN = 3,811 lbf

See THK catalog, page A-218 and A-219 for force directions equivalent loads and permissible moments.

However, the load ratings are well above the actual loads.

________________________________

Notes on Linear Bearing and Track:
"The high-end Minitech mills make use of THK recirculating rails and blocks for the ways."

THK rails can be butted end for end.

"The caveat to the use of linear Ball Bearing ways for a bench mill is that the leadscrew/bearing assembly must be totally rigid, with zero backlash. If there is backlash in the system, the low force requirements to move the table will cause all sorts of grief when the direction is reversed; in that moment, there is no load in the leadscrew, and the table will flop about like a dead fish under pressure from the cutter." ~ www.5bears.com Will a rack & gear have too much backlash?

THK RSR12 ways may be too small. THK HSR25 blocks and ways may be too big.

"20mm rails are a good all-around size for a medium benchtop mill."

___________________________

Suppliers of Linear Bearings and Track:

Quick Interchange Chart

THK - North America

IKO ~ http://www.am.nsk.com/default.asp?ID=124 , http://www.ikont.com/products.htm

NSK ~ http://www.ikont.com/catalog.htm

Igus ~ http://www.igus.com/drylin.asp
http://www.netmotion.com/htm_files/mc_slides_thom.htm
http://www.thomsonind.com/PDFs/Catalogs_and_Brochures/Linear_Guides_ProfileRail_catalog.pdf
www.techno-isel.com

LEE Controls, Inc. Roller Bearing Pillow Block Specifications ~ http://www.linearmotion.com/pb.html

Frelon Lined Bearings ~ http://www.qbcbearings.com/New/Frelon.htm

C1045 Cold Drawn Round Precision Shafting - Turned, Ground, & Polished ~ http://www.metalsdepot.com/products/coldfin2.phtml?page=cdround&LimAcc=

http://www.pacific-bearing.com/

HIWIN http://www.hiwin.com/lg/index.html

Motor:

Proposed Servomotor c/w Encoder ~ Item # 1480: This is the Tamagawa. The maximum speed is 3,000 rpm less actual voltage etc.

Perhaps a new motor c/w planetary gearbox should be used here?

Rack and Gear: Rack CNC 0059, Gear CNC 0058

What about thermal expansion on the X-axis of the table? If the rack is made of a material other than steel it will lengthen at a rate different from that of the table to which it is bolted.

"There is lots of previous posts on this here, 14 1/2 deg takes a larger load, 20 is a bit higher precision.Probabally 12 diametric pitch is the largest you may want to go with 20 about the smallest. Most large commercial gantrys use 14 1/2. Boston gear offer a economical way to go, In Canada they are carried by Bearing Supply."
Al.

The 20-degrees appears to be the preferred one.

The Machinery's Handbook, page 1916, says that for a Diametrical Pitch of 16 the pitch of the rack teeth is 0.1963. 6 ft rack will have 366.7855 teeth, Therefore exactly 366 teeth will be 366 * 0.1963 *25.4 = 1,824.8833mm.

This is a manufacturer of metric racks with mounting hols that match the THK track Looks like Module 5 is the answer http://www.atlantadrives.com/pdf/ads_racks.pdf

Calculations: The following is based on; the purchased linear table and the Mach3 manual, section 5.5.

The unit of measurement is metric.

The distance between 100 teeth on the rack is XX mm.

The number of teeth on the pinion N_S is XX.

The pinion's shaft revs per unit (mm) = 1 / (tooth pitch * N_S ) = XX.

The motor revs per unit = shaft revs per unit * N_S/ N_M= XX.

_________________________________

Calculations:

Gear Speed:

If the pinion is 1" diameter, then at the maximum speed of 132 fpm the pinion's speed will be (132fpm * 12") / (1 * 3.1429) = 504 rpm.
If the pinion is 2" diameter, then at the maximum speed of 132 fpm the pinion's speed will be (132fpm * 12") / (2 * 3.1429) = 252 rpm.

Reduction Ratio:

For 1" pinion diameter, the reduction between the motor and the pinion is 6:1 then the maximum servomotor speed (excluding 'catch-up' and acceleration and deceleration etc) will be 504 * 6 = 3,024 rpm. It has been mentioned that the maximum servomotor speeds are about 4,000 rpm. The maximum speed of the Tamagawa motor is 3,000 rpm less actual voltage etc.Catch-up is described in article of which I have hard copy. Page 6 of 8. Copy portion around 'servo lock' here. Define servo lock.

Acceleration and Deceleration:

Not done yet. Is there any reason for not having a slow acceleration and deceleration on the X-axis?

Motor Power Required:

1 HP = 33,000 foot-pounds per minute ~or~ 550 foot-pounds per second.

Unit:	Force; [F]	*	Distance: [u]	/	Time; [s]	=	Power [P]
English	25 lbf or ozf	*	132 foot or inch	/	1 minute or second	=	0.1 HP
		*		/		=	m-Kg/sec
metric SI	newton	*		/		=	joule
		*		/		=	Watts

For friction increase by 50% = 0.15 HP = 112 watts. This is probably way too light.

The purchased motor is 300W. The reduction ratio can be made low and the motor slowed down.

Encoder Specifications Required:

The motor turns at (3,024 rpm / (132 fpm * 12")) = 1.90909 revolutions for 1" linear movement.

The 0.0001" minimum move distance of will be 1.90909 * 0.0001 = 0.000190909 of a revolution = 1 / 0.000190909 = 1 / 5,238th of a revolution of the motor's shaft.

On a 1GHz PC, Mach3 can generate 35,000 pulses per second. On a faster PC, Mach3 can generate 45,000 pulses per second. (see Mach3, section 5.2.2) Since the rotation of the motor must be broken down into 5,235 segments a 1500 * 4(quadrature) = 6,000 PPR (Pulses Per Revolution) resolution will be needed. The Renco RM15 encoder maximum is 2.048 PPR. US digital E2 encoder maximum is 5,000 PPR.

In addition note that 45,000 / 6,000 is only 7.5 rps = 450 rpm. This is too slow.

I think that using the Gecko G340 with its Step Pulse Multiplier could double the pulses to the motor but this will halve the accuracy. In addition, the motor is not running fast enough.

_______________________________

"If the machine runs a rack and pinion drive mechanism you will probably need a gear reduction of about 6:1 to keep the motor speed up while maintaining a reasonable travel speed. Timing belts and pulleys make excellent and low cost gear reducers!" from http://www.machinetoolcamp.com/Servos%20and%20Amplifiers.htm

"If I were making a 4 foot router, I would use rack and pinion. When I was in business making CNC plasma cutting machines, we used rack and pinion exclusively. Rack and pinion is more tolerant of dirt, has 250 IPM (20.8 fpm) + speed capability (This is 6 times slower than what I want.), and can be readily setup as dual side drive by means of a cross shaft. You will have no "whip" problems which leadscrews experience above the critical speed. Rack with 20 degree pressure angle is preferred to 14-1/2 degree pressure angle. In fact, my test table is 32" x 36" and uses rack and pinion; I use it as a test table for the controller which I am making and for wood routing." ~ jcc3inc on CNCzone

Preliminary Rough Calculations: taken from Converting an Ordinary DC Motor to a Servomotor

Continuous torque [oz-in] = (HP / rotation [rpm]) * 10^6 = .25 / 1750) * 10^6 = 142.8 oz-in

Stall torque = 142.8 * 6 = 856.8 oz-in

2" PD pinion = 6.28" circumference.

If 11 ft of travel in 5 sec. is wanted

= 132" / 5 = 26.4" / sec.

= 26.4 * 60 = 1584" / min. ⁽¹⁾

= 1584 / 6.28 = 252.2 rpm ⁽¹⁾

(1) Does not take acceleration and deceleration into account.

1750 / 6.28 = 252.2 rpm
Gear reduction = 1750 / 252.2 = 6.9 : 1
Peak force = 856.8 * 6.9 = 5,944.6 oz = 371 lb. ⁽²⁾
Continuous force = 371 lb / 6 = 61.9 lb. ⁽²⁾

(2) Does not take friction into account.

What about a 2 speed (or 3 speed) reducer. High speed for filament winding of spar and slower speed(s) for filament winding of torque tube and milling of core and cured composite.

Or, what about timing belts and something that changes speeds.

Foam cores will be done faster and cleaner (no chips) with hot wire.

____________________________

Boston Gear ~ http://bostongear.com/products/open/spur.html

See Boston Gear catalog page 35 for 20º-pressure angle.

Which material is best; steel, brass, nylon, etc.

It appears that the 14-1/2º pressure angle has less backlash than the 20º pressure angle. This is the opposite of the previous posting on this web page.

No particular consideration has been given to the number of teeth in the gear.

________________________

Rack and Pinion Size Selection:

ref: Equivalent metric module = 25.4 / Diametral pitch | Equivalent Diametral pitch = 25.4 / Metric module

Calculations from Boston Gear Manual: (from p.138)

The backlash is 0.003" for a Diametral pitches between 14 and 32.

Gear: 20 Diametral pitch; 40 tooth; 2" PD; steel; Face width 0.5"; 20º pressure angle

Safe material stress (Steel; .20 carbon; Case-hardened) [lb/in^2] S = 25,000 Is the actual gear case hardened?

Face width [in] F = 0.5"

Tooth form factor Y = 0.389

Diametral pitch P = 20

Pitch line velocity [fpm] V = 40.2336 M/s (132 fpm). ~ Maximum speed.

If number of teeth was 20 then pitch dia. will be 1". Therefore for 132 fpm the pinion's speed will be (132fpm * 12") / (1 * 3.1429) = 504 rpm. If reduction is 6:1 then the maximum motor speed should be 3000 rpm. To this 'catch up' and acceleration and deceleration etc. will have to be added. Catch-up is described in article of which I have hard copy.

Tooth load [lb] W = (S * F * Y / P)(600 / (600 + V)) = (25000 * 0.5 * 0.389 / 20) * 0.82 = 199 lbs.

Maximum allowable torque = W * D / 2 = 199 * 2 / 2 = 199 lb-in

Maximum safe horsepower = W * V / 33,000 = 199 * 132 / 33000 = 0.8 hp = 588 W.

___________________ Alternative _________________

Gear: 16 Diametral pitch; 16 tooth; 1" PD; steel; Face width 0.75"; 20º pressure angle

Safe material stress (Steel; .20 carbon; Case-hardened) [lb/in^2] S = 25,000 Is the actual gear case hardened?

Face width [in] F = 0.75"

Tooth form factor Y = 0.295

Diametral pitch P = 16

Pitch line velocity [fpm] V = 40.2336 M/s (132 fpm). ~ Maximum speed.

Tooth load [lb] W = (S * F * Y / P)(600 / (600 + V)) = (25000 * 0.75 * 0.295 / 16) 345.7 + 0.82 = 283.4 lbs.

Maximum allowable torque = W * D / 2 = 283.4 * 1 / 2 = 141.7 lb-in

Maximum safe horsepower = W * V / 33,000 = 283.4 * 132 / 33000 = 01.13 hp = 845.6 W.

Rack and Pinion Sources:

Boston: See catalog.

Misumi ~ http://www.misumiusa.com/Catalog.aspx?CategoryID=-1,59910,60026 This company is said to be very good with good prices.

http://www.schlenkent.com/product6.html

http://www.andantex.com/racks.html

http://www.bostongear.com/products/open/spur.html#

NEXEN Roller Rack & Pinion ~ http://www.nexengroup.com/rp/ Interesting but not of value.

http://www.smallparts.com/products/descriptions/grs.cfm Said to have the best prices.

http://www.mcmaster.com/

Ball Screw Assembly: Forget, Going with Rack and Gear.

Notes:

The long screw will need one or two mid-braces, similar to the Thermwood one.
The proposed motor has a maximum RPM of 48V/50V * 3000RPM = 2880RPM. If the pitch is 10mm then the maximum travel speed is (2880RPM / 60sec) * 10mm = 48cm. = 18.8976" per second.

Two possible solutions to ballscrew use are, either use a fixed screw and rotating nut which makes screw whip a complete non-issue or "borrow" Thermwood's idea of spring loaded plastic dampers that press against the screw at a couple of points and flip out of the way when the carriage passes. Why would a rotating the nut be better than rack and pinion?

I think that chain and sprocket is no good since any chain stretch will really screw up the tolerances.

Reduction Unit:

Options:

Gearheads that Bolt to Servo Motor:

This is a possibility for the X-axis rack and pinion.

Planetary Gearheads; http://www.netmotion.com/htm_files/mc_slides_gear.htm

Gates ~ Mectrol: http://www.mectrol.com/

eBay ~ Listed in category: Business & Industrial > Search Results for 'Mectrol'

Applied Motion Products

http://www.applied-motion.com/products/gearheads/index.php

Micron

Parker:

Inline and right angle. Ratios from 3:1 to 100:1 are available in NEMA 23, 34 and 42 frame sizes.

http://www.daedalpositioning.com/products/Planetary_Gearheads__7067__30_32_80_567_29.html

_____________________________________

Timing belt and sheaves. NO. There is not enough room to put in a 6:1 reduction.

__________________________

Worm and wheel: Have high friction. NO. Use planetary gearing because it is more efficient and lighter.

Carriage for X to Y Axis:

The structure that is mounted on the THK bearing blocks and which supports the Y-axis linear slide, the X-axis drive etc.

Traverses the length of the table. (X-axis)
Incorporates Y-axis, Z-axis and C-axis movement.
Holds position very accurately in all four axes.
Must support weight and torque of other equipment, which is mounted on the carriage.
Can be driven by;

Accurate feed but slow

Rack and pinion
Ball screw
Infinite variable speeds or very large choice of ratios.

Less accurate feed but fast.

Cable and pulleys
A few different speed.
Multiple sheave diameters -or- vari-speed pulley.
Soft start and stop

Movable tray for electrical power, vacuum (for chip removal), Hydraulic, refrigerant for spools.

Make from steel plate and keep the weight down.
Locate home limit switch on X-axis pretty much inline with head of tools for accuracy.

Carriage for A-axis:

For notes see A-axis page.

Home and Travel Limit Sensors:
Consider using Parker Daedal units. This will give standardization on all three linear axes. Might also consider one of the units of the baby linear slide for A-axis home.

Cable Carrier:
Does current cable carrier have a large enough x-section for all power wires. control wires and vacuum tube?

Minimum of; 8 power, 11 control & tube.

Consider stopping the cable carrier back from the end and completing with a formed channel Or do this in the future.

Purchased on Ebay 7548132378

Kabelschlepp wire and cable carrier 0450.40 KR [Item 36]

Exact dimensions: Piece length (hinge to hinge) = 45mm. 82 pieces. Total length = 82 * 45 = 3,690mm = 145.27"Inside dimensions measure 27mm * 58 mm. Outside measures 34 mm 73 x mm. The inside dimension between the upper and lower strand is 220 mm.

Number of pieces in 180º bend = (220 + 34) * (22/7) / (2) / (45) = 8.87 = 9 pieces.

Maximum allowable travel = 82 - 9 = 73 pieces. 73 * 45mm = 3,285mm * 2 = 6,570mm

Information:

http://www.machinedesign.com/BDE/motion/bdemotion2/bdemotion2_9.html

http://www.designnews.com/article/CA85855.html

"Both pneumatic tubes (yellow = collet, blue = body) are routed, along with the power cable, in an "Igus" cable sheilding unit which reticulates like a snake as the spindle travels up and down." ~ www.5bears.com

Product:

http://www.igus.com/echain.asp

http://www.gortrac.com/

Nylatrac:- http://www.gortrac.com/nylatrac.htm

Miscellaneous:

The second 115VAC fan should be used to put a positive filtered pressure in THK and rack enclosure. The filter cover and power cable have also been purchased for it.

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Last Revised; January 31, 2007