# Thread: Spar building - cutting 45 degree corners in solid mast

1. Member
Join Date
May 2016
Location
Posts
98

## Spar building - cutting 45 degree corners in solid mast

Hi,

I'm currently in the middle of building spars for our sailboat, and was wondering if anybody had advice on how the make the 45 degree cuts on a solid timber spar. Our spare is 11.25 " diameter, 56 ' long so the 45 degree cuts are approximately 4.5 inches (to big for most skill saws)

I cut the tapers with a chainsaw, and then finished with an electric plane but I'm hesitating doing the same for the corners (It's pretty rough). The last spars we built for our old schooner where much smaller, so a 7.25 inch skilsaw almost made the cut, I just finished it with a hand saw. I've looked around for a rental of a beam saw, but that's not available locally.

Here is a link to our spar building :

http://boatmutts.ca/building-the-masts-and-spars/

Thoughts, Comments, Suggestions are welcome !

Mark
Last edited by Mark0; 07-17-2017 at 09:17 PM.

2. Senior Member
Join Date
Apr 2010
Location
South Australia and Tasmania
Posts
13,598

## Re: Spar building - cutting 45 degree corners in solid mast

A good hand saw will do it quicker than you might imagine. Chainsaw, wow, one mistake and you have to go find another tree! I think a picture of the boat is in order. A Lucas mill might be good, if there's a mobile sawyer anywhere near you?

3. ## Re: Spar building - cutting 45 degree corners in solid mast

Eight siding is easy if you make a gauge for the job. Basically it's a stick with two rods or dowels sticking down with space between a convenient bit larger than your largest side. Two scribes are set between such that the spaces between are, starting from one post to the nearest scribe, then scribe to scribe, then to the post have either 5-7-5 unit gaps or 7-10-7 gaps. Think of Pythagoras.

I am confused as to the mast diameter as it have a taper, but let's take 11-1/4" as the thickest and that you've tapered the sides and front to make a square section shape that has the side to side taper and the off the front taper but back side straight for the sail's luff.

11-1/4" is 45/4". The 5-7-5 requires 17 units while the 7-10-7 requires 27. You need something comfortably longer than the 11-1/4" and a total of 54 (twice the 7-10-7) is a bit more than the 51 of going thrice the 5-7-5. I'd go with the smaller.

So the stick will be have the three gaps of 15/4" - 21/4" - 15/4" or total space 12-3/4". Double check my arithmetic as this was in my head.

You lay the stick at an angle across a face and draw it along the length keeping the end posts in contact. As you get to tapered area, the angle of the stick will increase and the proportions being drawn will remain the same.

You get the idea. It marks for eight siding. It might be fastest to set your saw at 45 and cut off well outside your marked lines, planing to the line. Most people find that getting to 16 sides is easily done by eye but you should start by marking the centerline of each of the eight faces and using that reverence and the new corners you're making as references.

There have been many threads on this so someone will have a picture.

G'luck

4. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi,

I'm not worried about how to mark for the cut. I'm wondering the best way to make 200ft of a ~4 inches at 45 degrees.

Thanks !
Mark

5. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

My spar "shop" is across the road in an old unused barn (old tie stalls - so long and narrow) - it would be hard to set up a real lumber mill. A chainsaw isn't that bad, it's just pretty rough and I was looking for a better idea.

Mark

6. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi Phil,

I can't post a picture on the forum. I'd be kicked out...

http://boatmutts.ca/ (wife's website / blog)

Mark

7. Senior Member
Join Date
Mar 2011
Location
Mukilteo, WA
Posts
1,569

## Re: Spar building - cutting 45 degree corners in solid mast

Can you do the cuts from both sides? Assuming your marking went well, you should be able to cut halfway through from both sides with a standard circular saw and finish with a power plane.

You obviously have the ability to roll the spar already.

8. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi,

I have been thinking about that also (cuts from both sides). I went to see what Bud has to say, and his book literally fell open to page 33, which gives advice on how to do this with a skill saw. A 7.25 inch will still come up short, but would only leave an inch to do with a "hand ripper"

Cheers,
Mark

9. ## Re: Spar building - cutting 45 degree corners in solid mast

I get that the largest faces when eight sided will be more like under 3-1/2" Whatever. Just make whatever cut your saw will safely do and plane the rest. You could improve your speed by cutting the 45 with a 2" depth and then kerfing closer to the lines and knocking it down further with a slick. Or if you've used an adz, register chop across the grain and knock down with the grain as you go.

But it really does not take that long.

G'luck

10. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi Ian,

Strange, we get 4.66 inches. I'm a little embarrassed to say I don't understand how to plane after the cut or by what you mean by cutting the 45 with a 2" depth. I'm googling away on how to use a slick..

Cheers,
Mark

11. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

oh, I get it now about the planing after the cut. I was still thinking about the cut being made on the correct mark and then dealing with it being not being all the way through.

12. Senior Member
Join Date
May 2012
Location
Central Ohio
Posts
495

## Re: Spar building - cutting 45 degree corners in solid mast

Timber framers have larger 'skilsaws' that can get in deeper. I think Makita makes one, for example.
https://www.amazon.com/Makita-5402NA.../dp/B0000614UR
Rentable, fortunately.
6.25 at 90, 4 3/16" at 45.
A manly machine, so eat your Wheaties. Or build a Unistrut guide system.

Chip

13. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi Chip,

That was my first idea - but there are no rentals locally of these.

Mark

14. ## Re: Spar building - cutting 45 degree corners in solid mast

If you make a gauge 12" post to post and use the 7-10-7, then your distance each peg to its scribe are 3-1/2" and the center span between scribes is 5". This is handier for your spar.

If you set the saw to four inches and adjust the plate to 45 degrees and then cut the best corner you can with that having the blade coming out the bottom of your cut, not ploughing, you'll have just knocked off a good chunk of the corner but will be no where near your lines. Still, a lot of work out of the way.

The eight faces will actually be a bit less than 5" each and that's at the thick end, but just taking a 12" square for a moment and making an inscribed octagon, the distance from one original corner to the center of where a new face will be is 2-1/2". This is really not too much. So maybe the best approach would be to cut across each corner to a depth of 2" and a bit - just be sure you're not cutting past the line you've used the 8-siding gauge to make. You'll need to make the depth less as you proceed up the taper. Lots of short cuts across, like at most 1 per inch, maybe 1 per two inches so maybe 400 quick short cuts per edge. Then take a slick or your biggest chisel and knock the corners off. Finish plane to fit. This sounds like a lot but is likely considerably less stress on your saw than a long 45 degree cut.

G'luck

15. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi,

Here is a link to our spar building :

http://boatmutts.ca/building-the-masts-and-spars/

Mark

16. ## Re: Spar building - cutting 45 degree corners in solid mast

Good work.

17. Senior Member
Join Date
May 2012
Location
Central Ohio
Posts
495

## Re: Spar building - cutting 45 degree corners in solid mast

United Rental's website says they have it in Ottawa, ON, over on Sheffield. If you can believe their website...

https://www.unitedrentals.com/en/equ...aw-circular-16

Although that URL doesn't really scream Ottawa, though...

\$66 a day, \$200 a week.
They also have air and gas powered concrete saws that take up to 18" blades, which should get you in there nicely. You'd have to source a blade, and I don't know if the RPM's would be in the right ballpark.

A mid-size bandsaw on Unistrut track and rollers could easily make the necessary cuts, too. Rigging involved, but you've got a whole barn to work with.

Good luck!

Chip

18. ## Re: Spar building - cutting 45 degree corners in solid mast

Spar makers and shipwrights use an axe or an adze. A draw knife to clean up before the plane smooths it. It is not as though you are going to use the offcut for anything.

19. Senior Member
Join Date
Apr 2010
Location
South Australia and Tasmania
Posts
13,598

## Re: Spar building - cutting 45 degree corners in solid mast

Originally Posted by Mark0
Hi Phil,

I can't post a picture on the forum. I'd be kicked out...

http://boatmutts.ca/ (wife's website / blog)

Mark
Wow, she is going to be a lovely boat! Great work.

20. ## Re: Spar building - cutting 45 degree corners in solid mast

The pictures in your blog are nice and very helpful to understand what you are up to. Great Work.
You are probably all done by now but I will comment on how I would think about removing the corners of the square laminated timber.
Rather than make a saw cut the long way parallel to the centerline of the spar, I would:
(0) make many saw cuts perpendicular to the center axis of the spar so the big lump of undesired material can be easily broken out of the way and then very easily plane/shave the small amount to finish just past the bottom of the saw kerfs that are your indicator of the final dimension. Making close cuts across the grain always leaves weak pieces that can easily be broken out and the nature of the grain on a cross cut is such that when splitting out small pieces the runout/splitting does not travel into the good finished portion.
(1) mark the spar with the desired finished dimension.
(2) make many Many MANY saw cuts perpendicular to the centerline that barely touch the marks of the final desired dimension.
(3a) If you have made many saw cut close together the bits in between the cuts can be knocked and pried/popped off and then simply plane/shave until the saw kerfs disappear.
(3b) The many cross cuts can be done by eye with a handsaw carefully watching and coming close to the two marks of the final dimension, but on a big job a jig is very helpful.
The jig could be made to help one use either a handsaw or a powers/skilsaw and for 200' of cutting, a power saw seems the right thing.
So, A cradle made to lay on the point to the spar that is being flattened/shaved off that will slid along the length, can carry a skill saw and the saw can make cuts to the depth desired. . . . and then slide the cradle a fraction and cut, slid, cut , slide , cut, slide, cut and eventually ou have little bits that knock out and a small planing job ( and LOTS OF SAWDUST : )
(4) This all assumes that what you are sliding the jig along represents the finished shape/taper. If the finished dimension is not a constant distance from the corner of the timber (tapered) then hand sawing to the final dimension lines still works. One can still get power assist by power sawing just short of the final dimension lines and then just finish each of the (200ft x 24 cuts/ft=4800cuts) cut by eye with hand saw . . . : )
Last edited by George Ray; 07-17-2017 at 06:54 AM.

21. ## Re: Spar building - cutting 45 degree corners in solid mast

^ that is basically what you do with an axe

22. Senior Member
Join Date
Nov 2006
Posts
8,082

## Re: Spar building - cutting 45 degree corners in solid mast

Nice work.

If it had been me doing the job I would have made preliminary cuts close to the line with a skilsaw set to 45 degrees, sawing down the length of the mast. Cutting in from both sides would not get all the way through but the remainder could be easily cut with a sawzall running through both kerfs.

The advantage over a chainsaw, to my mind, would be less chance of a slip and getting a cleaner surface closer to the finished line...less to plane off and a more accurate surface on which to begin the planing.

Jim

23. ## Re: Spar building - cutting 45 degree corners in solid mast

Bob Smalser, formerly of these pages, has on his own site a most excellent eight-siding gauge.

Gnash teeth. His pix are at W.K.FineTools. com. Google 8-Siding or Octagon Marking Gage by Bob Smalser.

The end slides he makes are much superior to the dowels I use making up a quick&dirty gauge.

24. Senior Member
Join Date
Nov 2004
Location
Port Townsend WA
Posts
11,094

## Re: Spar building - cutting 45 degree corners in solid mast

I still use hand tools when shaping a spar. The only power tool is my trusty long sole Skill plane with its adjustable edge guide. A draw knife and adze are much safer than a chain saw! One slip can ruin your entire day! Use a quiet tool and listen to the sounds around you. Enjoy your work while you do! Smell the aroma of the wood!
Jay

25. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Originally Posted by Peerie Maa
Spar makers and shipwrights use an axe or an adze.
..... and the problem is I'm neither a spar maker or shipwright

26. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

[QUOTE=Chip Chester;5288921]United Rental's website says they have it in Ottawa, ON, over on Sheffield. If you can believe their website...

You can't believe their website. United doesn't have any in Canada at all.

Cheers,
Mark

27. Rocketman
Join Date
Apr 2000
Location
Posts
6,009

## Re: Spar building - cutting 45 degree corners in solid mast

Originally Posted by Mark0
..... and the problem is I'm neither a spar maker or shipwright
There should be cheap used ones like this

http://www.kijiji.ca/v-sailboat/osha...ationFlag=true

R

28. ## Re: Spar building - cutting 45 degree corners in solid mast

Originally Posted by Mark0
..... and the problem is I'm neither a spar maker or shipwright
It is really not that hard. You just got to know when to stop cutting.

29. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi,

Thanks to everybody for their time responding to my post. Lots of great ideas to pick from. We will be thinking about how we will tackle this over the next few days and I'll post back with the results.

Cheers,
Mark

30. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi,

I thought I would close the loop on this post and let everybody know how things went. I'm sure you have been waiting at the edge of your seat about the results

We decided to make the cut using our trusty 7.25" skill saw, from both sides and then use Jim's idea of running a sawzall to connect the two cuts. We already own a sawzall, and just purchased the largest saw we could find (12"), thinking it would give greater stiffness than something smaller. We also made up a 45 degree "foot" for the saw.

While making the cut I stayed about 5/16 inch from the line just in case things didn't line up. This should be pretty quick to plane off (haven't got to it yet).

After the first saw cut I followed Bud Mcintosh's advice in "how to build a wooden boat" on lining up saw cuts by drilling through the kerf with a long drill bit. It was a good double check, and things lined up pretty much with the scribe cut line on the adjacent face.

So here is the surprising bit. After rotating the mast and while making the second cut I realized the saw blade was connecting with the first cut, and I could feel this while guiding the saw. I didn't really expect this to happen, as the face length is 4.66 inches, and everything I saw online gave specs of the depth of cut at 45 degrees to be ~ 1 7/8 inch and under (depending on make/model). When I actually measured the depth of cut it was about 2.5 inches - so I am wondering what the manufacture's criteria is to determine this specification.

I'm actually glad I didn't have one of the big 16" beam saws - considering my spar bench height is 30", plus the 11.25" thick mast it would have been very difficult to manage.

I'd like to thank everybody for their posts - it has been very educational.

Cheers,
Mark

31. Senior Member
Join Date
Nov 2006
Posts
8,082

## Re: Spar building - cutting 45 degree corners in solid mast

Ya done good! How about a picture when it's done.

Jim

32. Member
Join Date
May 2016
Location
Posts
98

## Re: Spar building - cutting 45 degree corners in solid mast

Hi Jim,
The mast made it out of the spar shop today. Time for the mizzen....

mast and boat.jpg

Mark

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•