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A Single-fruitSeed Extractorfor Cucumbers

Todd C. Wehnerl andErvin G. Humphries2

Additional index words. Cucumissativus, mechanization, machinery,vegetable breeding, seed recovery

Summary. The construction of asingle-fruit seed extractor for cucum-ber is described. It increases the speedand ease of removing seeds fromindividual, mature cucumbers for laterdrying and planting. The machinesaves about 47 seconds/fruit com-pared to hand methods and is suitedto handling single fruit (or batches ofup to 50) by researchers needing seedsfrom controlled pollinations. In 5years of use, no reduction in seedrecovery or germination has beenobserved using the seed extractorrelative to hand harvest.

P lant breeding and biotech-nology research on cucum-ber (Cucumis sativus L.) often

requires that mature fruits be harvestedfor seed recovery from controlled pol-linations. We built and modified foursingle-fruit seed extractors at NorthCarolina State Univ., two of which areused currently by the cucumber breed-ing program in the harvest of over2200 fruit produced by controlled pol-lination each season. The machinesincrease the speed of seed harvest dsave labor costs compared to the handextraction methods previously used.

The single-fruit seed extractor wasbuilt by the Biological and Agricul-tural Engineering Shop at North Caro-

1Professor of horticultural science, North Carolina StateUniversity Raleigh, NC 27695.

2Professor of biological and agricultural engineering,North Carolina State University, Raleigh, NC 27695.

The use of trade names does not imply endorsement by theNorth Carolina AgriculturalResearch Service, norcriti-cism of similar owes not mentioned. We thank LeonardM. Pike for the originalprototype, Robert G. Gaines andTom Hill for machine construction. Rufus R. Horton.Jr., for machine testing, and David L. Vermillion for theillustrations. The cost of publishing this paper was de-frayed in part by the payment of page charges. Underpostal regulations, this paper therefore must be herebymarked advertisement solely to indicate this fact.

Fig. 1. Single-fruit seedextractor for cucumbers.

Fig. 2. Schematic diagram offrame and component parts of

single-fruit seed extraction.

lina State Univ. modeled after a ma-chine built by Leonard M. Pike (TexasA&M Univ., College Station). Our firstextractor (Fig. 1 ) subsequently wasmodified to make it more durable, easier

to maintain, and quieter. Some of thechanges made include the use of alumi-num and stainless steel to prevent rust,the addition of foam insulation insidethe hood for quieter operation, the useof bearings with a grease fitting forlubrication after each harvest season,and the replacement of the three wireson the augerwith three fins (or vanes) to

make the auger less likely to fail.Related machines. C u c u m b e r

seed harvest has become more mecha-nized in the last few years followingthe design of machines such as the seedsluice for small plots (Steiner andLetizia, 1986) and the bulk seed ex-tractor (Wehner et al., 1983). Thesingle-fruit seed extractor is similar inpurpose to the bulk seed extractor, butoperates on a different principle. Thebulk seed extractor (suitable for largequantities) crushes the fruit, creating alarge amount of pulp. After using thebulk extractor in a field isolation block,the mound of pulp and fragments ofdiscarded fruits can be disked into thefield. In contrast, the single-fruit seedextractor bores into the end of thefruit, leaving the fruit mostly intact foreasy disposal from the greenhouse orlaboratory where the extractor often isused.

Description. The essential com-ponents of the single-fruit seed extrac-tor are the extractor cone (or auger)for excavating the seed cavity and ameans to drive it, a pail or containment

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Table 1. Parts list and cost for constructing a single-fruit seed extractor for cucumberz.

zCosts are based on 1993 prices in Raleigh, NC.

vessel to collect the seeds, a strainer,and a suitable frame for support (Fig.2). In addition, it is useful to haveaccess to a water line with a nozzle

Fig. 3. Details of augerconstruction illustratingone of three vanes attachedto the center cover.

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(pistol grip garden hose type is ad-equate ) for flushing out the seeds andpulp from the pail. The tea strainer isan ordinary screen-wire kitchen type(diameter about 6 inches or 150 mm).A foot-operated on–off switch for thedrive motor is recommended to free

both hands of the operator for othertasks. The cost of construction, in-cluding labor and the component partsand materials, was more than $800 in1993 (Table 1). Costs would be less ifthe aluminum and stainless-steel ma-terials were replaced with less-expen-sive alternatives and labor from withinthe project was available.

The single-hit extractor unit is34 inches high x 12 inches wide x 26inches deep (864 x 305 x 660 mm).The frame design (Fig. 2 ) is simple:the main consideration is supportingthe motor, pail, and drive shaft at aninclination of about 45° to facilitatedraining and wash-out. Ideally, theframe should fit inside a sink or someother drain-equipped fixture to dis-pose of the wash water conveniently .Frame members are 1 × 1 × 3/16 inch(25 × 25 × 4.76 mm) aluminum angleswelded together to form a rigid sup-port. Stainless-steel angles also wouldbe suitable, but mild steel is not rec-ommended since the unit is frequentlywet.

The 0.5-inch (12.7-mm) diam-eter drive shaft is supported by twoself-aligning pillow block bearings andis driven by an A-section V-belt via a0.25 -horsepower (0.187-kW),l15-V-AC, 1725-rpm electric motor. Thedrive shaft also must be supported

HortTechnology • July/Sept. 1995 5(3)

Fig, 4. Schematic of three different augers; Ais the original three-vane stainless steelauger; B is constructed in a similar mannerfrom PVC materials; and C is a commer-cially available soil-boring tool having asingle vane or blade. All three augers areapproximately the same size.

Table 2. Time required for each operation of seed extraction from cucumbers using band (knifeto cut fruit, spoon to remove seeds) and machine (single-fruit extractor) methodsz.

Time (see/fruit) for fruit IotaMethod Operation 1 2 3 4 5 Mean

Hand c u t 45 45 50 50 50 48Extract 1 5 20 1 5 15 1 5 16Wash 8 5 90 90 125 115 101Total 145 1 5 5 155 190 180 165

Machine cut 0 0 0 0 0 0Extract 1 5 20 20 20 15 18Wash 70 65 115 145 105 100Total 85 85 135 165 120 118

zData are means of five lots of fruits measured for the three operations required for seed extraction.

axially to resist the thrust loads as fruitare pushed onto and removed fromthe auger. Thrust loads are relativelysmall, and the bearings can absorbthem provided the bearings are se-curely locked to the drive shaft. Motorspeed is reduced by the 2.0/3.5 sheaveratio to drive’” the auger at 986 rpm.Evaluation at other speeds indicatedthat an auger speed as low as 600 rpmalso might be satisfactory.

Torque requirements on the au-ger drive shaft varied as a function offruit maturity and rate of feed. We didnot encounter torque levels above 15inch-pounds (1.7 Nm). The drivemotor was mounted on a hinged platethat allowed adjustment of tension inthe drive belt. Belt tension should bemaintained at a level just sufficient todrive the auger; higher belt tensionincreases the likelihood of injury to theoperator if hand, arm, or clothingshould become entangled with theauger.

A rigid coupling with two set screws

at each end is attached to the base of theauger core shaft (Fig. 3) to attach theauger to the end of the drive shaft afterits assembly through the bottom of thepail. It is important to mount the 5-gallon (18.9-liter) polyethylene pail rig-idly to the frame to maintain alignmentof the drive shaft and the center hole inthe pail.

The stainless-steel auger (Fig. 3)was the most difficult component tofabricate. Three vanes constructed from16-gauge stainless steel were attachedin a spiral to a 0.625-inch (16-mm)diameter stainless-steel core shaft, 12inches (305 mm) long. Each vane spi-raled 120° from its base to its tip and

was welded (noncontinuous fillet) tothe core. The core shaft was cone-tipped (Fig. 4) to provide easy pen-etration of the fruit. The base of thecore shaft was drilled-out 2.5 inches(63.5 mm) deep to accept the 0.5-inch(12.7-mm) diameter drive shaft. Bend-ing the varies and attaching them uni-formly to the core to form a balancedauger required more than novice skillsin metal fabrication. Silicon caulking,or something more durable, should beused to seal any gaps between thevanes and core that might trap seedsand permit them to be mixed withsubsequently processed fruits.

The frame, motor, and drive com-ponents were enclosed with a 22-gauges t a i n l e s s - s t e e l s h e e t ( F i g . 1 )undercoated with 0.5-inch (12.7-mm)thick extruded polystyrene insulation.Those steps were taken to protect theelectrical connections and motor frominadvertent wetting by the wash-outnozzle and to dampen the noise of thedrive components. Proper groundingof the electrical system is required. Inaddition, a ground fault interruptershould be used in the circuit to elimi-nate the possibility of shock.

Operation. Fruit are harvested 4to 7 (usually 6) weeks after pollinationand are allowed to age up to 3 days.The seeds are extracted from one fruitat a time, the bucket and auger arewashed clean of seeds using a hosewith a nozzle. and the seeds are col-lected in a kitchen-type tea strainerunder the bucket. Next, the seeds arewashed using a blast of water from thehose, light seeds are floated over thetop of the strainer in a bucket of waterin the sink, and the remaining seeds arewashed again using a second series ofwater blasts from the hose. Finally,seeds are placed in a 100-mm-diam-eter, plastic petri plate bottom (theshallower lid is not used). Seeds in

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Fig. 5. Schematic of an experimental direct-drive unit that also uses a slip clutch betweenthe drive motor and seed extractor auger.

petri plates are held in a screen-bottomtray in a seed dryer and dried at 30C.After drying, the seeds are placed incoin envelopes for storage.

The time required for extractionwas 15 to 20 see/fruit (mean of 18 )and 60 to 150 sec/fruit (mean of 100)for washing, averaging 120 see/fruit.Washing times of 60 to 80 sec/fruitwere possible if the fruit had been offthe vine for 1 or more days. Fruit heldat room temperature after harvest be-gin enzymatic breakdown of tissue sothat seeds separate easily from the pla-cents during extraction and washing.Harvesting fruit from plants and drying of seeds from the extraction pro-cess required additional time.

Some plant breeders harvest fruitmore than 1 week before extraction topermit cleanup of the cucumber plantsand replanting the greenhouse. Sincethe seeds apparently are continuing tomature in the detached fruit, the over-lap permits a shorter generation timein the greenhouse.

The hand method of seed extrac-tion involved cutting the fruit openlongitudinally with a knife, scrapingthe seeds out with a spoon, and wash-ing them in a tea strainer under a water

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spray. Time required for hand extrac-tion was 140% that of the machinemethod (Table 2). Hand washing (65to 145 sec/fruit, mean of 100) re-quired about the same time as machineextraction (85 to 125 see/fruit, meanof 101 ), so the major gain was made inseed removal, which required 60 to 65sec/fruit (mean of 64). With the hand-extraction method, it required 45 to50 see/fruit (mean of 48 ) to cut a fruitopen, and 15 to 20 see/fruit (mean of16) to remove the seeds. With themachine, only 18 see/fruit were re-quired to cut into the fruit and removethe seeds in a single operation.

Seed extraction from single fruitusing hand vs. the machine showed thatthe machine extractor saved 47 see/fruit. That saving amounts to 89 h ( 11worker-days) per year for our three cropsof 2268 fruits each.

Performance. The single-fruitseed extractor has been used for 5 yearswithout problem and without injuryto the operators. The percentage ofseeds recovered from single fruit, andthe germination speed and percentagewere apparently unaffected by thesingle-fruit extractor. However, we rec-ognize that the extractor could besimplified with regard to construction,especially the auger. Also, improve-ments related to safety are necessaryfor general use. Modifications to the

unit to address those concerns havebeen considered and to a limited ex-tent evaluated.

We were able to simplify con-struction of the auger by using polyvi-nyl chloride plastic (PVC). The corewas a length of 0.5-inch (13-mm)schedule 80 PVC pipe, and the vaneswere 0.5 × 0.5-inch (12.7 × 12.7-mm)square PVC bars (Fig. 4). Hot-air PVCwelding methods were used to attachthe vanes to the core. The auger tipwas formed in a lathe from solid, round0.75-inch (19-mm) diameter PVCstock and attached ‘to the pipe corewith PVC adhesive. The base of theauger core was fitted with a steel insertto allow its attachment to the driveshaft. The PVC auger was tested brieflyand it performed similarly to the stain-less-steel auger extracting seeds andpulp. The vane edges were beveled0.0625 inch ( 1.6 mm) and were con-siderably less likely to injure theoperator’s hand compared to the 16-gauge, stainless-steel vanes.

A third auger was tested to im-prove the simplicity of construction. Itconsisted of a commercially availablesoil-coring tool manufactured byJISCO and available at nursery outlets.It had a single flight or vane of 14-gauge alloy steel spirally wound on a0.3 125-inch (8-mm) diameter corewith a 2-inch (51-mm) pitch to form a1.5-inch (38-mm) diameter auger (Fig.4). We modified the ends of the unitand its length to mount it to the driveshaft of the extractor. The auger, re-quiring the least amount of fabricationas a seed extractor, also performedsatisfactorily in limited tests.

The primary safety concern regard-ing the extractor was the potential con-tact of the operator’s hand with therotating auger, or the possibility of catch-ing and wrapping loose clothing in theauger. Short sleeve shirts or blouses arerecommended, and rings, wrist watchesor other accessories should not be wornwhen operating the extractor. Addi-tionally, a safety feature to disengage theunit from its power source when itencounters out-of-the-ordinary condi-tions should be considered. To this end,we installed a slip clutch on the driveshaft of a modified unit (Fig. 5).

The in-line clutch (model JJ-28;W.W. Berg) was adjusted to slip attorque levels from 11 to 187.4 inch-ounces (0.0779 to 1.33 Nm) by vary-ing the spring pressure applied to theclutch surfaces. Shaft bore size was

limited to 0.3125 inch (8 mm) andmodifications of the drive shaft to in-clude a rigid step-down coupling werenecessary. Note that the drive motorwas positioned to an in-line position,thereby eliminating the V-belt drive(Fig. 5). In that configuration, a mo-tor should be selected with a rotationalspeed of 600 to 1000 rpm. The clutchunit, although rated at < 240 inch-ounces (1.7 Nm, previously deter-mined), was successful in driving the

JISCO auger in limited tests. Moreimportantly, the clutch mechanism al-lowed one to grasp the auger and stopit by hand. Its inclusion (or a similarunit) in the drive train as an in-linecomponent, or mounted directly tothe motor shaft in an indirect drivemode, should be considered by poten-tial builders and users of the extractor.

Plans. Working drawings of thesingle-fruit extractor will by suppliedby T.C. Wehner upon request.

Literature Cited

Hughes, G. R., C. W. Averre, and K.A. Sorensen.1983. Growing picking cucumbers in NorthCarolina. N.C. Agr. Ext. Serv. AG-315.

Steiner, J.J. and B.F. Letizia. 1986. A seed-cleaning sluice for fleshy-fruited vegetables fromsmall plots. HortScience 21:1066-1067.

Wehner, T. C., G.E. Tolls, and E. G. Humphries.1983. A plot scale extractor for cucumber seeds.HortScience 18:246-247.

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