Author Topic: Building a model Drag Saw  (Read 6874 times)

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #15 on: August 29, 2018, 03:47:38 PM »
Crueby--will probably put a 1/16" pin thru one of the dogs in the blue gear that fits into a shallow round slot in the shaft extender it runs on. that lets the gear rotate freely but stops it from sliding away from the shoulder it rides against.

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #16 on: August 29, 2018, 08:31:51 PM »
I've spent 6 hours today in "geometry world", coming up with a set of linkages that will work for the drag saw. I know of no set of equations that will let you calculate this stuff. It is more "try it and see" engineering. What I have here is a set of linkages that go through all of the required motions without binding or going into a "lock" position. Now I have to take the time to do a visual comparison between what I have and what a real drag-saw looks like. This is fun stuff, but it isn't easy. Before I cut any metal, I will build these linkages full scale in cardboard and using "stick pins" work it through all of the required motions.

Offline Jasonb

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Re: Building a model Drag Saw
« Reply #17 on: August 29, 2018, 08:49:15 PM »
Brian now that you have added the second shaft it may be easier to have the dog clutch on the sproket end of your lay shaft. That way the pinion gear can fit onto the existing engines crank without the need for extending it and the slower speed will mean less crunching when you engage the clutch plus you have an untouched shaft to start with.

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #18 on: August 30, 2018, 12:34:07 AM »
I am having second thoughts about using the Kerzel engine with the drag saw. The Kerzel has a 3/4" bore, while the Odds and Ends engine has a 1" bore, larger flywheels, and is all around a bigger engine. I'm looking at the size of the Kerzel compared to the larger  Odds and Ends hit and miss engine and I think the Odds and Ends engine would be a better choice.

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #19 on: August 30, 2018, 12:36:03 AM »
Jason--You are right, but there are too many things rotating around the face of the disc on the second shaft to give me room there for a dog clutch.

Offline Jasonb

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Re: Building a model Drag Saw
« Reply #20 on: August 30, 2018, 07:00:09 AM »
Brian I mean the lay shaft with the large gear/small chain sproket which has nothing in the way

Offline Robert Hornby

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Re: Building a model Drag Saw
« Reply #21 on: August 30, 2018, 07:20:49 AM »
Here's one I made earlier.

Robert
Age and treachery will always overcome youth and skill

Offline gbritnell

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Re: Building a model Drag Saw
« Reply #22 on: August 30, 2018, 12:50:07 PM »
Beautiful display Robert!
Gbritnell
Talent unshared is talent wasted.

Offline b.lindsey

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Re: Building a model Drag Saw
« Reply #23 on: August 30, 2018, 03:08:07 PM »
Beautiful Robert!! That must get a lot of attention at shows.

Bill

Offline J.L.

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Re: Building a model Drag Saw
« Reply #24 on: August 30, 2018, 03:12:49 PM »
Hi Robert,

Stunning display.

John

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #25 on: August 30, 2018, 03:31:51 PM »
Robert--Lovely job. 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

Offline Kim

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Re: Building a model Drag Saw
« Reply #26 on: August 30, 2018, 05:41:28 PM »
That is very cool, Robert!
Love having the boiler, engine and saw all on the same display. And the little row of cut-off disks showing the work of the saw is great!
Kim

Offline Brian Rupnow

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Re: Building a model Drag Saw
« Reply #27 on: August 30, 2018, 05:41:52 PM »
Okay--Got that sorted. The engine is now the Philip Duclos "Odds and Ends" hit and miss engine. In order to get from 1000 rpm at the crankshaft to 84 rpm at the disc which the saw arm attaches, and to fit the constraints of what I have, there are actually two gear reductions coming off the engine shaft and one roller chain reduction. Part of the reason there are two gear reductions is to get the disc spinning the same clockwise rotation of the engine, and to get that large 108 tooth pulley with the spokes far enough away from the engine crankshaft to enable getting a cross shaft underneath the engine to reach the far side of the engine where the chain and sprockets will be. I haven't changed anything on the drive disc and linkages which are shown.

Offline Ye-Ole Steam Dude

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Re: Building a model Drag Saw
« Reply #28 on: August 30, 2018, 05:49:22 PM »
Looks great Brian, this will be a fun project to follow.

Have a great day,
Thomas

Offline Jasonb

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Re: Building a model Drag Saw
« Reply #29 on: August 30, 2018, 05:51:51 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.