Author Topic: Building a model Drag Saw  (Read 5944 times)

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #30 on: August 30, 2018, 06:19:16 PM »
That small yellow gear won't do anything in the way of reduction, it's just acting as an idler, could be any size you like and won't affect the ratios.
I'm not sure you are right. The smallest gear is a 20 tooth on the crankshaft. The yellow gear directly below it is a 30 tooth. When the crankshaft gear does one revolution, the yellow gear will only make 0.666 revolutions. The 108 tooth gear below the 30 tooth yellow gear will only turn 0.2777 turns when the yellow gear revolves once. so--Total reduction from crank gear to 108 tooth gear is 5.4:1.
when the 108 tooth gear rotates once, the crankshaft will rotate 5.4 times.

Offline Alyn Foundry

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Re: Building a model Drag Saw
« Reply #31 on: August 30, 2018, 06:33:47 PM »
Hi Brian.

Jason is quite correct, that gear is purely an idler. In fact on early " high class " engines they made the intermediate gear with an odd tooth number, this reduced the wear in one place as each valve was lifted.

That intermediate wheel simply reverses the rotation between primary and secondary wheels, one tooth in one tooth out.

Cheers Graham.

Offline Jasonb

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Re: Building a model Drag Saw
« Reply #32 on: August 30, 2018, 06:59:14 PM »
Brian, just look back at your earler post or do the maths again 108/20 also equals 5.4

http://www.modelenginemaker.com/index.php/topic,8396.msg181692.html#msg181692

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #33 on: August 30, 2018, 08:36:35 PM »
I pulled the flywheel off of the starter side of the Odds and Ends hit and miss engine. It appears that I will be able to make my dog clutch work on this side and still be able to use my electric drill starter. I am proceeding with more layout work on the drag saw mechanism and frame.

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #34 on: August 30, 2018, 08:39:25 PM »
Yes Jason--You were right.  I thought there might be something a bit fishy about what I was saying, although it sounded good to me ---at first.---Brian

Offline JC54

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Re: Building a model Drag Saw
« Reply #35 on: August 30, 2018, 08:54:39 PM »
 Just love the display Robert, all together like that shows the complete system, especially if you wish to explain it to someone at a show/display. Maybe a newbie  :shrug: :thinking: :cartwheel:

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #36 on: August 31, 2018, 12:31:04 AM »
This thing is going to be big!! I'm pretty sure I have all the calculations right. The log is 3" diameter which is fairly close "scale-wise". The keyhole saw I inherited from my father and haven't used in 20 years is going to provide the blade for this beast.


Offline zeeprogrammer

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Re: Building a model Drag Saw
« Reply #37 on: August 31, 2018, 12:45:00 AM »
I'm along for the ride.  :popcorn:
An engine is great. An engine doing work is really great.

Robert's model is certainly an inspiration.
Carl (aka Zee) Will sometimes respond to 'hey' but never 'hey you'.
"To work. To work."
Zee-Another Thread Trasher.

Offline Robert Hornby

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Re: Building a model Drag Saw
« Reply #38 on: August 31, 2018, 02:33:19 AM »
Brian

 I can't see clearly--the rope that lifts the saw goes over a pulley block on top of the mast, and I can't see where it goes from there. Does it go back down to a winch system? --Brian


The "rope" attaches via a pulley block to the cross head guide. The end of the rope goes around the hand winch.

Robert
Age and treachery will always overcome youth and skill

Offline Jasonb

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Re: Building a model Drag Saw
« Reply #39 on: August 31, 2018, 06:59:15 AM »
Brian, as has been mentioned before you really want a blade that cuts on the PULL stroke and that pad saw won't unless you intend to cut it down and drill for fixings at the other end. If the blade sticks when it is pushed it will buckle but that won't happen when it is being pulled as it will be in tension. Small bow saw blade or a cut down Japanese saw or a tree pruning saw will do. These can be cut down and a hole added and will look the part.

https://www.dictum.com/en/japanese-saws-baaa/replacement-blade-for-akagashi-universal-270-kataba-universal-270-712986

That may also affect the direction you run in as the engine end of the saw wants to go downwards on the pull stroke.
« Last Edit: August 31, 2018, 07:32:58 AM by Jasonb »

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #40 on: August 31, 2018, 01:34:01 PM »
Jason--My intent was to cut this blade down and taper it in the other direction to what is shown. That way it will be cutting on the pull stroke. If that doesn't work (it's free) then I will buy the one in your link. Thank you.---Brian

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #41 on: August 31, 2018, 02:28:46 PM »
Someone said that a journey of 1000 miles begins with one step. The only thing on this drag saw that I haven't made before is the "dog clutch". So---that is where I will begin. The design is going to be marginally different from the one in the attached 3D model because of minor differences in the output shaft on the Odds and Ends engine from the Kerzel.

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #42 on: September 02, 2018, 08:26:39 PM »
Today I machined the crankshaft extension for the Odds and Ends engine. There is more to this extension than meets the eye. It has two counterbores machined on the far end, one to precisely fit the flywheel hub, and one to match the 1/2" length of crankshaft that extended past the flywheel hub. The end you can't see is drilled and tapped six places to match the clearance holes in the flywheel. You can see that in the pulley I removed in order to fit the extension on. In a perfect world, there will be no wobble in the end of that shaft extension when the engine is running. The 20 tooth gear, bushing, and drive dog will all be fitted to this extension. I machined two grooves in the large outside diameter of the extension  in case I want at some point to drive o-ring drive belts with this engine.

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #43 on: September 03, 2018, 07:40:12 PM »
Today has been mostly cad work, figuring out the overall layout, how part A connects to point B, etcetera. I still have to find room for a gas tank, as the one currently on the Odds and Ends engine will be in the way. I'm liking this. The log being sawed is 3" diameter.


Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #44 on: September 03, 2018, 10:14:51 PM »
This shows the dog clutch lever  by itself and how it assembles to the drag saw, where it pivots on the axle. It moves very little to engage or disengage the dog clutch. Right now I'm not sure how to make it stay "in gear" or "disengaged". There isnt enough movement to use ball detents`. Maybe a couple of spring washers and a bolt through the bottom pivot?