Author Topic: Shaft compression...why?  (Read 785 times)

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Offline Todd Mathis

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Shaft compression...why?
« on: November 12, 2019, 08:41:14 am »
Ok guys!  Everyone here knows I'm a goober with most wood except bamboo.  Could someone please explain WHY we would compress a wooden shaft?  Is it to remove irregularities in the wood?  I am very curious why this is done.  I'm guessing that when I go to Rose City and buy a set of cedar shafts, those will come perfectly straight, right?  Is this for wood I might harvest to make arrows with?

Offline Pat B

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Re: Shaft compression...why?
« Reply #1 on: November 12, 2019, 08:48:02 am »
Todd, I think compressing wood shafts helps to stabilize the shaft which helps to keep it straight.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Deerhunter21

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Re: Shaft compression...why?
« Reply #2 on: November 12, 2019, 09:09:52 am »
wait, do you mean compression straightening, or compressing the whole shaft?
"Only when the last tree has died and the last river been poisoned and the last fish been caught will we realise we cannot eat money." Cree Native-American Proverb

A amature practices untill he gets it right. A master practices untill he never gets it wrong.

Russell - 15 years

Offline PEARL DRUMS/PEARLY/PD/DRUMS

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Re: Shaft compression...why?
« Reply #3 on: November 12, 2019, 09:55:50 am »
The whole shaft gets compressed. Example, take a 23/64 shaft and run it through a heated up compression block and make it an 11/32. I can only assume the shafts are much harder as the fibers are compressed. Some of the best POC shafts I ever toucher were old Acme compressed stock. I think the quality of those old shafts was in the grain structure more so than the compression. 
Only when the last tree has died and the last river has been poisoned and the last fish has been caught will we realize we cannot eat money.

Offline Pat B

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Re: Shaft compression...why?
« Reply #4 on: November 12, 2019, 10:00:59 am »
One thing to remember about compressed shafts is they don't take stain very well after compressing so if you plan on staining your shafts do so before compressing them. If you are just going to crown dip and crest with paint you can do that after compressing and the paint sits on top and doesn't sink into the wood.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline mikebarg

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Re: Shaft compression...why?
« Reply #5 on: November 12, 2019, 11:20:03 am »
Does anyone know of any videos out there showing the compression process?

Offline Pat B

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Re: Shaft compression...why?
« Reply #6 on: November 12, 2019, 12:35:19 pm »
I think 3Rivers sells a compression block. I have poplar shafts Charlie Jefferson sent me. I think he chucked the end of the shaft in an electric drill and drove them through the tapered hole in the compression block. As the shaft is spun and compressed it heats up which also burnishes the shaft. The company that makes the compression block may have a video or you could check out You Tube.
Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline TSA

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Re: Shaft compression...why?
« Reply #7 on: November 14, 2019, 12:13:58 pm »
if i may be so bold as to offer some input here.
some fact, some opinion, and some conjecture  ;D )P(

so there are two types of compression here- besides the "compression straightening"

1. as P D says, where a good shaft is reduced in size by using a compression block.

heres something to bear in mind with spine, it is dictated , primarily by two principle factors
 a. the actual chord depth, so like a roof truss, the deeper the chord, the greater the stiffness, in turn the bigger the diameter of a  tube, the greater the stiffness.
b. the greater the quantity of material, the greater the stiffness.
both these factors work hand in hand, as when you increase the diameter of a dowel, so you also inadvertently also increase the volume of material.
However based on my experience the volume of material seems to be the greatest factor at play- any engineers please give input!

so, in turn,  if you take a 23/64 shaft, and you reduce it to 11/32 you should retain a lot of the higher spine value of the original 23/64. due to the fact that you have retained all the original material, but simply reduced the diameter a wee bit.
 in my experience you lose a bit of spine, but not as much as if you were going to simply sand it to 11/32, removing the extra material for good.

many shafts are also burnished, because the maker cant, or wont sand them.
As the dowel exits from the cutter heads, marginally oversize, they are then immediately put through a compression block ( same machine , compression block is right behind the dowel head). to reduce them to final size, and to create a smooth surface, as the cutters leave a rough surface.

Pitchy woods like Pine, are really difficult to sand, so they are doweled oversize, then compressed to final size.

then compression process no. 2.
this is full compression of the wood, ie: the old Sweetland Forgewood process.
 Where an entire flitch ( board) is compressed by a factor of as much as 3 ( in other words a 3" thick  board compressed to 1" thick),  blanks are cut from this processed board, and then shafts spun up from the blanks.
Pro's of this process are incredibly high spine in smaller diameters- Bill Sweetland was getting 100# shafts in 5/16, but they do come with  higher mass, which is not entirely a bad thing for hunting.
they are tough, durable, and of very high spine.

contrary to some misinformation out there, the POC is not the only wood able to be compressed, Bill ran many tests, he like the POC best, but many other woods were equally suitable.
he even compressed Western Red Cedar , to such an extent that it wouldnt float!!
i have seen some hemlock shafts made by this process, and they performed incredibly well.

cheers ;)
« Last Edit: November 18, 2019, 04:30:54 pm by TSA »

Offline Todd Mathis

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Re: Shaft compression...why?
« Reply #8 on: November 23, 2019, 12:14:15 pm »
wait, do you mean compression straightening, or compressing the whole shaft?
I'm actually not sure...I have been reading here and other places about compressing wooden shafts, and I was wondering why they do this. 

Offline Todd Mathis

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Re: Shaft compression...why?
« Reply #9 on: November 23, 2019, 12:16:39 pm »
if i may be so bold as to offer some input here.
some fact, some opinion, and some conjecture  ;D )P(

so there are two types of compression here- besides the "compression straightening"

1. as P D says, where a good shaft is reduced in size by using a compression block.

heres something to bear in mind with spine, it is dictated , primarily by two principle factors
 a. the actual chord depth, so like a roof truss, the deeper the chord, the greater the stiffness, in turn the bigger the diameter of a  tube, the greater the stiffness.
b. the greater the quantity of material, the greater the stiffness.
both these factors work hand in hand, as when you increase the diameter of a dowel, so you also inadvertently also increase the volume of material.
However based on my experience the volume of material seems to be the greatest factor at play- any engineers please give input!

so, in turn,  if you take a 23/64 shaft, and you reduce it to 11/32 you should retain a lot of the higher spine value of the original 23/64. due to the fact that you have retained all the original material, but simply reduced the diameter a wee bit.
 in my experience you lose a bit of spine, but not as much as if you were going to simply sand it to 11/32, removing the extra material for good.

many shafts are also burnished, because the maker cant, or wont sand them.
As the dowel exits from the cutter heads, marginally oversize, they are then immediately put through a compression block ( same machine , compression block is right behind the dowel head). to reduce them to final size, and to create a smooth surface, as the cutters leave a rough surface.

Pitchy woods like Pine, are really difficult to sand, so they are doweled oversize, then compressed to final size.

then compression process no. 2.
this is full compression of the wood, ie: the old Sweetland Forgewood process.
 Where an entire flitch ( board) is compressed by a factor of as much as 3 ( in other words a 3" thick  board compressed to 1" thick),  blanks are cut from this processed board, and then shafts spun up from the blanks.
Pro's of this process are incredibly high spine in smaller diameters- Bill Sweetland was getting 100# shafts in 5/16, but they do come with  higher mass, which is not entirely a bad thing for hunting.
they are tough, durable, and of very high spine.

contrary to some misinformation out there, the POC is not the only wood able to be compressed, Bill ran many tests, he like the POC best, but many other woods were equally suitable.
he even compressed Western Red Cedar , to such an extent that it wouldnt float!!
i have seen some hemlock shafts made by this process, and they performed incredibly well.

cheers ;)
Thanks very much!   I think I have a better understanding now.  Don't know if if means anything for bamboo, but I do LOVE to shoot wooden shafts.

Offline Todd Mathis

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Re: Shaft compression...why?
« Reply #10 on: December 05, 2019, 07:16:26 am »
The whole shaft gets compressed. Example, take a 23/64 shaft and run it through a heated up compression block and make it an 11/32. I can only assume the shafts are much harder as the fibers are compressed. Some of the best POC shafts I ever toucher were old Acme compressed stock. I think the quality of those old shafts was in the grain structure more so than the compression.
This would make all the sense in the world.  I assume they shaft would be tougher too.

Offline TSA

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Re: Shaft compression...why?
« Reply #11 on: December 05, 2019, 10:56:50 am »
bear in mind that many shafts are already compressed coming from the manufacturer, in other words.
 as a manufacturer you have two options of finishing your shafts, either you sand them, or you compress them, both have their pros and cons. but the biggest one is pitchy wood wont sand!

now compressing through a block, is to a larger degree only compressing an outer layer or shell on the shaft, the heat and pressure is not going in very deep.
it is a great tool.
 you are essentially getting the spine and mass ( and most of the "toughness") of a 23/64 shaft , but in an 11/32 diameter shaft!
to compress an entire shaft is another story all together :OK
« Last Edit: December 06, 2019, 04:33:16 pm by TSA »