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THREAD CHASING - TROUBLESHOOTING
Ernie Newman
Useful videos by Sam Angelo and Alan Stratton.
https://www.youtube.com/watch?v=uDevNqlnQlw
https://www.youtube.com/watch?v=MZhPt8xmM1w
https://www.youtube.com/watch?v=T2cOJ8k1PUw
Thread won’t start
A series of grooves form, not a thread.
Try less forward pressure when feeding the chaser across the surface of the wood. The chaser should just graze the surface. If the chaser is held lightly then the second tooth falls into the almost invisible groove cut by the first tooth. This allows the chaser to find it’s own speed automatically. We don’t know the correct rate that the chaser should move across the surface so we need to let the chaser slow or accelerate as it’s trailing teeth slip into the groove. A firm grip is a disadvantage as it over-rules this process. “We are chasing threads, we are not going to catch them by getting tough.” Bill Jones.
Hold chaser held parallel to chamfer for initial passes then gradually align with lathe bed
It is important that tat least two teeth contact the wood at a time.
Threads break up – wood selection
The wood may be the problem. It needs to be very hard and fully seasoned with straight, fine, even grain. It should be free of splits, knots, voids, wavy grain and interlocked grain. The grain runs between centres but see segmented rings below.
Good species - Boxwood, Pink ivory, African Blackwood, Lignum Vitae, Ebony Reasonable species i- Desert Ironwood, Cocobolo, Osage Orange, hard Maple and some fine Rosewoods. Poor wood will sometimes take a thread if strengthened by glue.
Good Australian species include: Mulga [Acacia aneura], Gidgee [Acacia cambagei], Bullock Bush [Queensland Inland Rosewood], NT Ironwood, Cooktown Ironwood [Erythrophleum chlorostachys], Sandalwood [Santalum spicatum], False Sandalwood [Plum Bush or Goldenwood], Western Myall [Acacia paprocarpa], WA Quandong [Santalum accuminata], WA Native Currant [Cantheum latifolia], Red Ironbark, Red Morrell [Euc lLongicornis], Cypress Pine [Callitris glauca], some Eucalypts.
Practice material Candle wax is excellent for practice. As is medium density fibreboard [MDF]. Wear a dust mask. MDF inserts can be threaded, stained and then glued into a box made from wood that won’t take a thread. Use dust protection when working MDF. Inserts may also be made from good chasing species and from PVC pipe, plastic, corian, horn and polyethylene from chopping boards.
Another reason that threads break is that too much pressure is applied, especially when threads reach their full depth. Rather than taking heavy cuts with a chaser it is better to remove wood by turning off the crowns, leaving the bottom of the threads, then chasing again. Threads may also break if the chaser is blunt. Hone or grind the top of the chaser.
Segmented rings
See two videos by Alan Stratton
https://www.youtube.com/watch?v=SWyHyLdeDCo&feature=youtu.be
NB fingers too near bandsaw in this video
https://www.youtube.com/watch?v=1b4aPiFnELo&list=RDCMUCucYlCYbbf1ZDGO-7OjKl5w
Chaser jerks
File, sand and wax the toolrest.
Smooth and wax the underneath of the chaser.
There may be a defect in the wood – see thread breaks up above
Drunken [wobbly] threads often still work if the fit is sloppy.
Drunken threads may develop if the lathe speed is too slow.
Double threads
If the threads are too close together just keep going, usually one thread will eventually dominate. If this fails then turn off the double thread and start again.
Sometimes double-start threads appear. Here the threads are the right distance apart but there are two separate threads. These threads slope much more steeply than normal threads when viewed from the side. They form when the chaser traverses twice as fast as normal. Turn them off and start again.
Tool moves sideways too quickly
Slow the lathe or use a finer chaser. Speeds between 100 and 500 rpm work reasonably well but 250-300 is ideal.
Check for double-start threads – see above.
Lid won’t screw fully on
Check if threads are tapered. Place a steel rule on the thread and visually line it up with the lathe bed. Re-cut threads till they are parallel to the lathe bed. If the female chaser isn’t held parallel to the floor then the thread will be tapered.
If the threads are parallel then one of them may need to be deepened. A sloppy fit is better than a tight one.
Fit tightens overnight
The wood may not have been fully seasoned. Sometimes even seasoned wood will move after turning as stresses are released. In this case it is often possible to remount the box on the lathe and cut the threads a little deeper. They may even be deepened by holding the box in your hand and running the chaser around the thread by hand.
Beginning of the thread is damaged
This is often caused by a stationary start. Take a running start by positioning the chaser a few millimetres away from the rounded shoulder so that it hits the shoulder on the move. The beginning of the thread is usually removed later so damage here doesn’t matter much.
Start with the chaser teeth angled about parallel to the chamfer and gradually correct till it is parallel to the lathe axis. At least two teeth should be in contact with the wood initially.
Grain doesn’t match
Remove wood in tiny increments from outside of female thread or male shoulder.
Fit is too loose
Make two boxes. Turn a new lid for the base and a new base for the lid.
MORE ON CHASING
Using chasers to add decorative grooves
It is easy to cut parallel decorative grooves in the rim of a platter, around a spindle or all over a turning using a chaser. The chaser is presented to the wood without moving sideways. This technique works on most species if the cut is light and gradual. If the wood is painted before the grooves are cut then sharp bands of colour will emerge.
Decorative spirals may be chased into the end grain of many species. This can be a striking feature on spinning tops.
What size chaser is best?
Fine chasers [16-24 TPI - teeth per inch] are easier when starting out. Coarser threads are easier to see but take more skill, especially if the lathe won’t run slowly. Very fine threads tend to cross thread in use.
What is the best shape for a box?
It is a good idea to enlarge the box inside the opening as this provides clearance when cutting the female thread.
How are the diameters of the two parts of a box calculated?This depends on the chaser size. Lets assume that the male thread is chased first and that the chasers are 16 TPI. The outside of the male thread should be about 1.5 mm [1/16”] larger in diameter than the diameter of the recess for the female thread. This way, if the first attempt to chase the female thread is unsuccessful there is enough wood for a second or third attempt.
If the chasers are finer than 16TPI then the difference between the two diameters can be a little less than 1.5 mm [1/16”]. For example the difference could be 1mm [1/25”] for 24 TPI chasers. If the chasers are coaser than 16TPI then the difference between the two diameters could be greater. For example the difference could be 2mm [1/12”] for 10 TPI chasers.
Making and buying chasers
Commercial chasers are expensive. Workable chasers can be made from bolts but it is better to use die head chasers. Email me [email protected] re die heads.
A low-tech way to slow the lathe
An old motor may be used to create low speeds to make chasing easier. Turn a wooden pulley about 300 mm [12”] in diameter and attach it securely to the left-hand side of the headstock spindle. Turn a second pulley about 38 mm [1 ½”] in diameter, attach it to a motor mounted behind the lathe and connect the pulleys with a belt. Disengage the regular motor belt and run the lathe with the second motor. The suggested pulley sizes will run a 1400 rpm motor at about 150 rpm and a 1700 rpm motor at about 190 rpm. Chasing is a gentle process so the motor can be low powered.
Chasing with the motor reversed
When chasing the male [outside] thread it can be tricky to remove the chaser just before it hits the shoulder to the left of the thread. If the chaser hits the shoulder it may damage the thread. If you can reverse the direction of the lathe and stand at the back of the lathe then it is possible to cut the male thread away from the shoulder rather than towards it. This may prove easier than the standard method.
Segmented rings
See two videos by Alan Stratton
https://www.youtube.com/watch?v=SWyHyLdeDCo&feature=youtu.be
NB fingers too near bandsaw in this video
https://www.youtube.com/watch?v=1b4aPiFnELo&list=RDCMUCucYlCYbbf1ZDGO-7OjKl5w
Example
25 x 25 x 250mm square section [this includes extra length for safe handling]
Long side 40 – short side 12
Method 1
Cut 6 segments at 60 degrees with a table-saw using a stopper to set length
Glue all 6 at once with a band clamp
Or press glue one segment at a time to form trios then sand both trios on table sander
Method 2
Mark 6 segments at 60 degrees with a 60-degree set square and cut all slightly oversize then sand to lines with table sander
press glue one segment at a time to form trios then sand both trios on table sander
Method 3
Combine table-saw and bandsaw
Acknowledgements
Bill Jones, Fred Holder, Keith Rowley, Mike Darlow, Mike Mahoney, Gordon Ward, Ken Cooper, Alan Stratton, Sam Angelo.
THREAD CHASING - TROUBLESHOOTING
Ernie Newman
Useful videos by Sam Angelo and Alan Stratton.
https://www.youtube.com/watch?v=uDevNqlnQlw
https://www.youtube.com/watch?v=MZhPt8xmM1w
https://www.youtube.com/watch?v=T2cOJ8k1PUw
Thread won’t start
A series of grooves form, not a thread.
Try less forward pressure when feeding the chaser across the surface of the wood. The chaser should just graze the surface. If the chaser is held lightly then the second tooth falls into the almost invisible groove cut by the first tooth. This allows the chaser to find it’s own speed automatically. We don’t know the correct rate that the chaser should move across the surface so we need to let the chaser slow or accelerate as it’s trailing teeth slip into the groove. A firm grip is a disadvantage as it over-rules this process. “We are chasing threads, we are not going to catch them by getting tough.” Bill Jones.
Hold chaser held parallel to chamfer for initial passes then gradually align with lathe bed
It is important that tat least two teeth contact the wood at a time.
Threads break up – wood selection
The wood may be the problem. It needs to be very hard and fully seasoned with straight, fine, even grain. It should be free of splits, knots, voids, wavy grain and interlocked grain. The grain runs between centres but see segmented rings below.
Good species - Boxwood, Pink ivory, African Blackwood, Lignum Vitae, Ebony Reasonable species i- Desert Ironwood, Cocobolo, Osage Orange, hard Maple and some fine Rosewoods. Poor wood will sometimes take a thread if strengthened by glue.
Good Australian species include: Mulga [Acacia aneura], Gidgee [Acacia cambagei], Bullock Bush [Queensland Inland Rosewood], NT Ironwood, Cooktown Ironwood [Erythrophleum chlorostachys], Sandalwood [Santalum spicatum], False Sandalwood [Plum Bush or Goldenwood], Western Myall [Acacia paprocarpa], WA Quandong [Santalum accuminata], WA Native Currant [Cantheum latifolia], Red Ironbark, Red Morrell [Euc lLongicornis], Cypress Pine [Callitris glauca], some Eucalypts.
Practice material Candle wax is excellent for practice. As is medium density fibreboard [MDF]. Wear a dust mask. MDF inserts can be threaded, stained and then glued into a box made from wood that won’t take a thread. Use dust protection when working MDF. Inserts may also be made from good chasing species and from PVC pipe, plastic, corian, horn and polyethylene from chopping boards.
Another reason that threads break is that too much pressure is applied, especially when threads reach their full depth. Rather than taking heavy cuts with a chaser it is better to remove wood by turning off the crowns, leaving the bottom of the threads, then chasing again. Threads may also break if the chaser is blunt. Hone or grind the top of the chaser.
Segmented rings
See two videos by Alan Stratton
https://www.youtube.com/watch?v=SWyHyLdeDCo&feature=youtu.be
NB fingers too near bandsaw in this video
https://www.youtube.com/watch?v=1b4aPiFnELo&list=RDCMUCucYlCYbbf1ZDGO-7OjKl5w
Chaser jerks
File, sand and wax the toolrest.
Smooth and wax the underneath of the chaser.
There may be a defect in the wood – see thread breaks up above
Drunken [wobbly] threads often still work if the fit is sloppy.
Drunken threads may develop if the lathe speed is too slow.
Double threads
If the threads are too close together just keep going, usually one thread will eventually dominate. If this fails then turn off the double thread and start again.
Sometimes double-start threads appear. Here the threads are the right distance apart but there are two separate threads. These threads slope much more steeply than normal threads when viewed from the side. They form when the chaser traverses twice as fast as normal. Turn them off and start again.
Tool moves sideways too quickly
Slow the lathe or use a finer chaser. Speeds between 100 and 500 rpm work reasonably well but 250-300 is ideal.
Check for double-start threads – see above.
Lid won’t screw fully on
Check if threads are tapered. Place a steel rule on the thread and visually line it up with the lathe bed. Re-cut threads till they are parallel to the lathe bed. If the female chaser isn’t held parallel to the floor then the thread will be tapered.
If the threads are parallel then one of them may need to be deepened. A sloppy fit is better than a tight one.
Fit tightens overnight
The wood may not have been fully seasoned. Sometimes even seasoned wood will move after turning as stresses are released. In this case it is often possible to remount the box on the lathe and cut the threads a little deeper. They may even be deepened by holding the box in your hand and running the chaser around the thread by hand.
Beginning of the thread is damaged
This is often caused by a stationary start. Take a running start by positioning the chaser a few millimetres away from the rounded shoulder so that it hits the shoulder on the move. The beginning of the thread is usually removed later so damage here doesn’t matter much.
Start with the chaser teeth angled about parallel to the chamfer and gradually correct till it is parallel to the lathe axis. At least two teeth should be in contact with the wood initially.
Grain doesn’t match
Remove wood in tiny increments from outside of female thread or male shoulder.
Fit is too loose
Make two boxes. Turn a new lid for the base and a new base for the lid.
MORE ON CHASING
Using chasers to add decorative grooves
It is easy to cut parallel decorative grooves in the rim of a platter, around a spindle or all over a turning using a chaser. The chaser is presented to the wood without moving sideways. This technique works on most species if the cut is light and gradual. If the wood is painted before the grooves are cut then sharp bands of colour will emerge.
Decorative spirals may be chased into the end grain of many species. This can be a striking feature on spinning tops.
What size chaser is best?
Fine chasers [16-24 TPI - teeth per inch] are easier when starting out. Coarser threads are easier to see but take more skill, especially if the lathe won’t run slowly. Very fine threads tend to cross thread in use.
What is the best shape for a box?
It is a good idea to enlarge the box inside the opening as this provides clearance when cutting the female thread.
How are the diameters of the two parts of a box calculated?This depends on the chaser size. Lets assume that the male thread is chased first and that the chasers are 16 TPI. The outside of the male thread should be about 1.5 mm [1/16”] larger in diameter than the diameter of the recess for the female thread. This way, if the first attempt to chase the female thread is unsuccessful there is enough wood for a second or third attempt.
If the chasers are finer than 16TPI then the difference between the two diameters can be a little less than 1.5 mm [1/16”]. For example the difference could be 1mm [1/25”] for 24 TPI chasers. If the chasers are coaser than 16TPI then the difference between the two diameters could be greater. For example the difference could be 2mm [1/12”] for 10 TPI chasers.
Making and buying chasers
Commercial chasers are expensive. Workable chasers can be made from bolts but it is better to use die head chasers. Email me [email protected] re die heads.
A low-tech way to slow the lathe
An old motor may be used to create low speeds to make chasing easier. Turn a wooden pulley about 300 mm [12”] in diameter and attach it securely to the left-hand side of the headstock spindle. Turn a second pulley about 38 mm [1 ½”] in diameter, attach it to a motor mounted behind the lathe and connect the pulleys with a belt. Disengage the regular motor belt and run the lathe with the second motor. The suggested pulley sizes will run a 1400 rpm motor at about 150 rpm and a 1700 rpm motor at about 190 rpm. Chasing is a gentle process so the motor can be low powered.
Chasing with the motor reversed
When chasing the male [outside] thread it can be tricky to remove the chaser just before it hits the shoulder to the left of the thread. If the chaser hits the shoulder it may damage the thread. If you can reverse the direction of the lathe and stand at the back of the lathe then it is possible to cut the male thread away from the shoulder rather than towards it. This may prove easier than the standard method.
Segmented rings
See two videos by Alan Stratton
https://www.youtube.com/watch?v=SWyHyLdeDCo&feature=youtu.be
NB fingers too near bandsaw in this video
https://www.youtube.com/watch?v=1b4aPiFnELo&list=RDCMUCucYlCYbbf1ZDGO-7OjKl5w
Example
25 x 25 x 250mm square section [this includes extra length for safe handling]
Long side 40 – short side 12
Method 1
Cut 6 segments at 60 degrees with a table-saw using a stopper to set length
Glue all 6 at once with a band clamp
Or press glue one segment at a time to form trios then sand both trios on table sander
Method 2
Mark 6 segments at 60 degrees with a 60-degree set square and cut all slightly oversize then sand to lines with table sander
press glue one segment at a time to form trios then sand both trios on table sander
Method 3
Combine table-saw and bandsaw
Acknowledgements
Bill Jones, Fred Holder, Keith Rowley, Mike Darlow, Mike Mahoney, Gordon Ward, Ken Cooper, Alan Stratton, Sam Angelo.