JET 719100 Manuel d'utilisation et d'entretien télécharger pdf (Page 18)

Checks and Cracks

Green wood will check and crack. For best results,

leave logs in as long a length as you can handle.

As the material starts to dry, surface cracks will

develop on the ends of the log. Cut off two to three

inches and you should find good, sound wood.

Also cut the log in half along the pith to avoid

having it in the finished piece. Most checks radiate

from the pith.

As you turn bowls from green wood, make sure

you maintain a consistent wall thickness

throughout the piece. Leaving a piece thick in

some areas and thin in others will cause the wood

to dry unevenly and promote checks and cracks.

Distortion

Distortion is a problem associated with turning

green wood. It will vary from one type of wood to

the next. Typically, fruitwoods tend to distort more

than others. It also varies with the time of year the

tree was cut and how the logs are stored.

Tools for Bowl Turning

The deep fluted bowl gouge is the most essential

and versatile tool for most bowl and plate turning.

The bowl gouge is heavier and easier to control

than other types of gouges. It also allows removal

of wood much faster and with less vibration than

other gouges. Most average sized bowl work can

be accomplished with a 3/8" or 1/2" bowl gouge. A

1/4" bowl gouge is best suited for smaller bowls

and light finishing cuts. Larger 3/4" and 1" bowl

gouges are only used for extremely large pieces.

Large domed scrapers can also be used to help

clean up the interior surfaces of bowls. A light

touch with the scraper slightly tilted will eliminate

some of the ridges occasionally left by an

inexperienced bowl gouge.

11.5 Bowl Turning Techniques

To Shape Outside of Bowl

1. Odd shaped burls, crotches and other irregular

shaped blanks require special preparation

before mounting in a chuck or onto a

faceplate. Remove the bark, if there is any,

from what appears to be the center of the top

of the workpiece.

2. Drive spur center into the top of the workpiece

with a mallet or dead blow hammer.

3. Slip the spur center into the headstock taper

and bring the tailstock with a live or ball

bearing center into position. Lock the tailstock

to the bed and advance the tailstock spindle in

order to seat the cup center into the

workpiece. Tighten the ram locking handle.

4. Turn workpiece by hand to ensure proper

clearance.

5. Start lathe at lowest speed and bring it up to

the maximum safe speed for the size of work

to be turned. If the machine starts to vibrate,

lower the speed until vibration stops.

6. Rough out the outside of the bowl with the 1/2"

deep fluted bowl gouge, holding the handle of

the tool firmly against your hip. For best

control, use your whole body to move the

gouge through the workpiece.

7. As the bowl takes shape, work on the bottom

(tailstock end) to accomodate attaching a face

plate.

8. Turn a short tenon (about 1/8" long) the size of

the hole in the faceplate. See Figure 27. This

will allow centering the workpiece when the

faceplate is attached.

Figure 27

(NOTE: If you plan to use a chuck, turn a

tenon of the appropriate length and diameter

to fit your chuck.)

9. Stop the lathe, remove workpiece and attach

face plate or chuck (see Section 11.4,

"Mounting Stock").

The surfaces of faceplate and

workpiece should mount flush to each other.

10. Finish turning the outside of bowl with 1/2" or

3/8" bowl gouge. Leave additional material at

base of bowl for support while turning interior.

This will be removed later.

To Shape Interior of Bowl

1. Stop the lathe and move tailstock away. (You

may want to remove the center from the

tailstock to avoid bumping it with your elbow.)

2. Adjust tool support in front of the bowl just

below centerline, at a right angle to the lathe

ways.

3. Rotate workpiece by hand to check clearance.

4. Face off top of bowl by making a light shearing

cut across the top of workpiece, from rim to

center.

5. Place 1/2" bowl gouge on tool support at

center of the workpiece with the flute facing

top of bowl. The tool handle should be level

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JET 719100 Manuel d'utilisation et d'entretien Page 18

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