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James Combs
11-14-2018, 8:34 PM
I make a lot of ornamental birdhouses and a few skep looking beehives. When turning the bases of the houses and the top of the hives I have always used a wooden shop made mandrel. I have actually broken the wooden one in the past. The pic on the left is of a repaired break.
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The wooden one has served me well making onsey twosey or even half a dozen ornaments but I recently got an order for 92 of them. I use a one inch carbide Forstner bit to bore the inside of the houses, works great except that the ID of of the bores even with the same bit varies slightly with wood specie. My solution in the past has been to add or remove a layer of plastic electrical tape to maintain a tight enough fit for turning the wood. Long story short, I got tired of taping and un-taping. I decided I needed an adjustable mandrel so I chucked up a chunk of aluminum in my metal lathe, with some turning, drilling, and sawing I came up with this.

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It has slots in the side walls that vane like pieces of 1/8" UHMW can be pushed out against the inner wall of the BH blank. These two pics only show one set of slots but another set was added 90degrees to this set after the photo. You can see two of the four vanes in the pic above. The end cap screws onto the end with an internal thread and captures the four sections of aluminum plus the ends of the UHMW vanes. The second pic shows the cap in place. The extra aluminum in the chuck was turned away later.
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This tapered pen is eventually threaded just behind the taper and is screwed into and out of the mandrel to raise and lower the vanes. The vanes were initially cut over size in diameter of the mandrel, they were sticking out of the mandrel by about an 1/8". I set the initial lowered height of the vanes by having the tapered pin retracted to its max retract position then turning off all of exposed UHMW flush with the aluminum of the mandrel.
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Then I cut slots around the circumference of the mandrel, through the aluminum and the vanes to fit in o-rings. The o-rings are 5-10 thousandths proud of the vanes and mandrel with the whole mandrel being just under one inch in diameter. When the tapered pen is screwed in it lifts the vanes and the o-rings against the ornament blank wall holding the blank tightly on the mandrel. The o-rings serve two purposes, they add friction plus they hold one end of the vanes inside the mandrel body, as mentioned a cap holds the other ends.
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The hardest part of making this thing was cutting the 1-1/4"-8tpi threads in the lathe end of the mandrel. My shoulders were sore for two days after completing that task.
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Since making and using the mandrel I have turned about 20 ornaments with it and it works great, absolutely no tape required. lol ;-)

Thanks for looking and C&C appreciated.

John K Jordan
11-14-2018, 9:52 PM
Wow, great design and job! That looks like the cadilac of expanding mandrels, certainly ready for heavy production.
Isn't it nice to have a metal lathe and mill on hand!

I've never used any UHMW material but plenty of HDPE.

Do you source aluminum for things like this? A metal recycling place near here, Nobel Metals, sells metals at close to scrap prices and you never know what they will have - I've found some big chunks of aluminum as well as rods and plates, sometimes brass, bronze, plenty of stainless and mild steel, and once some titanium tubing at give-away prices. I got the HDPE sheets there, maybe 4'x6'x1", which someone sold as scrap after a shape was cut out. Once I found a box full of surgical instruments like scissors, hemostats, bone hammers, and things I couldn't guess. They also have a building full of a huge variety of new hardware at scrap prices. Everyone around here who builds gizmos checks there periodically (if they know about it!). Yikes, I see they have a bunch of square steel tubing in - I need to go tomorrow! https://www.noblemetalsonline.com/

I've held things similar to your bird houses with wooden mandrels, the old time-honored pin jaw method (a mandrel with a flat and a small diameter pin that rolls on the flat to jam the work), and the Nova 17mm pin jaws. The extended length Nova jaws hold well in a hole but they might be a tiny bit to big - I didn't measure but the web site says the OD is 25.9mm. I've made mandrels from wood that expanded by driving a screw into the center but they probably wouldn't hold up to that many bird houses, even if made with dogwood or lignum vitae.

I can't imagine going into woodturning production like you mention - if faced with doing 92 of anything I think I'd go crazy. (Sounds too much like work. :)) If someone is ordering them to resell they must really be in demand. Have you posted pictures of some here? I'd love to see some - I'll try a search.

JKJ

Marvin Hasenak
11-15-2018, 2:16 PM
I use a similar system, but I cheat and use the expanding arbors from Breakheart Tool, they were originally bought for game call mandrels, but they work great for mini bird houses. Drill the blank with a 3/4" hole for the inside, then a 1/2" hole at the bottom for the finial.

James Combs
11-15-2018, 8:49 PM
Wow, great design and job! That looks like the cadilac of expanding mandrels, certainly ready for heavy production.
Isn't it nice to have a metal lathe and mill on hand!

I've never used any UHMW material but plenty of HDPE.

Do you source aluminum for things like this? A metal recycling place near here, Nobel Metals, sells metals at close to scrap prices and you never know what they will have - I've found some big chunks of aluminum as well as rods and plates, sometimes brass, bronze, plenty of stainless and mild steel, and once some titanium tubing at give-away prices. I got the HDPE sheets there, maybe 4'x6'x1", which someone sold as scrap after a shape was cut out. Once I found a box full of surgical instruments like scissors, hemostats, bone hammers, and things I couldn't guess. They also have a building full of a huge variety of new hardware at scrap prices. Everyone around here who builds gizmos checks there periodically (if they know about it!). Yikes, I see they have a bunch of square steel tubing in - I need to go tomorrow! https://www.noblemetalsonline.com/

I've held things similar to your bird houses with wooden mandrels, the old time-honored pin jaw method (a mandrel with a flat and a small diameter pin that rolls on the flat to jam the work), and the Nova 17mm pin jaws. The extended length Nova jaws hold well in a hole but they might be a tiny bit to big - I didn't measure but the web site says the OD is 25.9mm. I've made mandrels from wood that expanded by driving a screw into the center but they probably wouldn't hold up to that many bird houses, even if made with dogwood or lignum vitae.

I can't imagine going into woodturning production like you mention - if faced with doing 92 of anything I think I'd go crazy. (Sounds too much like work. :)) If someone is ordering them to resell they must really be in demand. Have you posted pictures of some here? I'd love to see some - I'll try a search.

JKJ
Thanks for the comments John. Most of my materials are from recycling also but just stuff I have found and have been given, never thought about "buying" from a recyclable, got one at about 25 miles, Stuffs Recycling, will have to check them out. I got this aluminum from a friend, did a little work for him and he made a donation. Probably have a life time supply of UHMW in various thicknesses, use it for a lot of jigs and fixtures. Makes great guides when fitted in miter tracks on my table saw. On the 92 ornaments, don't do a lot for folks outside the family anymore but this was for a charitable organization, one that has diabetes cure as a goal, got a Granddaughter with diabetes and had to help out. Past production was at the most 20 or so for a Sister. I will add a post over in the turner's forum after this showing some pics of the ornaments.


I use a similar system, but I cheat and use the expanding arbors from Breakheart Tool, they were originally bought for game call mandrels, but they work great for mini bird houses. Drill the blank with a 3/4" hole for the inside, then a 1/2" hole at the bottom for the finial.
Hi Marvin, thanks for looking and commenting. I actually looked at a set of those arbors before I decided to make my own. The only problem I saw with them other than $$, was the expansion method. I rarely make birdhouse ornaments with a lower finial and would not have access to the expansion screw. That is the reason my expansion pin is adjusted through the lathe spindle. As I mentioned to John Jordan above I will post some pics of the completed ornament, you will see what I mean. Using the new mandrel, adding a bottom finial would be no problem and I have made a few like that, actually I think there is one in the combo pic I will be posting. I think it was the result of a design change "opportunity". lol ;)

Marvin Hasenak
11-15-2018, 9:38 PM
I now see why you wanted the mandrel your way.