stand-up hold-down.

[Jacob]

Before I bodge one up of my own design I thought I'd ask on here if anybody has a design or good ideas for a stand-up hold-down.
What I want to do is rough carving on a bench top but with a foot operated hold-down, for speed and convenience as compared to screw down bench hold-fasts, or to sitting at a shave horse etc.
What I envisage is a post attached to the back of my joinery bench, with a pivoted beam coming across to the front, pulled down by a foot pedal connected with a piece of rope, with a counterweight or spring to pull it back up. You'd either set the beam at the height for the workpiece so it'd pin the thing directly to the bench, or have something attached at the end of the beam - some sort of dangling leg?
If you see what I mean. :shock:

 

[bugbear]

Without the gearing of a screw thread or cam, I'm not convinced you'd get enough force to hold the workpiece for vigorous carving. Shavehorses provide some leverage, but also only have to resist forces in pretty much one direction, unlike 3D carving.

Further, carvers working on 3D objects move around a lot, which would make having one of your feet in a fixed position to operate the gadget irksome.

What are you carving? There may be good solutions to particular problems, even if the general problem is hard.

BugBear

 

[Jacob]

... There may be good solutions to particular problems, even if the general problem is hard.

BugBear

You give up too easily BB! :lol:
The general problem is easy - you can have as much leverage as you want according to position of pivot points and linkages. The particular problem isn't difficult either, it's only a variation on the shave horse or carvers horse. I can work one out but it's always handy to see other people's designs first.

 

[Richard T]

I think using rope might let you down as it will always have some stretch. I'd recommend a steel/iron pivoted rod instead.

 

[bugbear]

... There may be good solutions to particular problems, even if the general problem is hard.

BugBear

You give up too easily BB! :lol:
The general problem is easy - you can have as much leverage as you want according to position of pivot points and linkages.

Yes, but that reduces movement. More of one, less of the other.

The particular problem isn't difficult either, it's only a variation on the shave horse or carvers horse. I can work one out but it's always handy to see other people's designs first.

I look forward to your WIP (photos compulsory).

I don't recall seeing anything like you're describing in my reading, so it'll be interesting. Oh - and you didn't say what you were carving?

BugBear

 

[Jacob]

... There may be good solutions to particular problems, even if the general problem is hard.

BugBear

You give up too easily BB! :lol:
The general problem is easy - you can have as much leverage as you want according to position of pivot points and linkages.

Yes, but that reduces movement. More of one, less of the other......

So screws, bolts, jacks, gears, levers of all sorts, are totally useless and will never catch on? :roll:

 

[Pete W]

If you see what I mean. :shock:

I'm not sure I do, but would something like this do the job:
http://www.frontiernet.net/~dmatt/shavepony/

 

[Jacob]

Yes that's the sort of thing except that's more for legs, spars etc with not enough clearance for misshapen blocks. I am wondering about something which comes down from above like an ordinary bench hold-fast but foot operated and spring or weight released.

 

[AndyT]

Another well-established approach which might be adaptable is the sort of foot strap used by file cutters:

Very quick and easy to reposition, and non-marking, I'd have thought.

 

[bugbear]

So screws, bolts, jacks, gears, levers of all sorts, are totally useless and will never catch on?

1) To clamp a complex object in multiple positions requires a clamping surface that can move a good deal.

2) To clamp something firmly against force from all directions requires high pressure.

3) As I understand your requirment, the source of the clamping force is a single foot stroke.

If you gear down (3) to fulfill (2) you defeat (1). Simples.

Unless there are other factors to your problem you haven't told us - which is why I asked what you were carving. Some things are easier to hold than others.

BugBear

 

[Jacob]

So screws, bolts, jacks, gears, levers of all sorts, are totally useless and will never catch on?

1) To clamp a complex object in multiple positions requires a clamping surface that can move a good deal.

2) To clamp something firmly against force from all directions requires high pressure.

3) As I understand your requirment, the source of the clamping force is a single foot stroke.

If you gear down (3) to fulfill (2) you defeat (1).

No you don't. :roll:

Unless there are other factors to your problem you haven't told us - which is why I asked what you were carving. Some things are easier to hold than others.

BugBear

I'm thinking of having a crack at a gnome.

 

[xy mosian]

One of the foot operated vices, looks as if it is running along the top of a tall saw horse, uses a ratchet to apply force and a kicker plate to release. Or have I dreamt it? Now if that arrangement were vertical ... would that come anywhere near?
I think the vice was Triton, but could very well be wrong.

xy

 

[No skills]

Thats what I was thinking, Jaw horse??

 

[No skills]

Yes, Jawhorse.

http://www.amazon.co.uk/s/?ie=UTF8&keyw ... vio6e3w3_b

 

[Jacob]

ooh yes! But I was hoping to bodge something up with offcuts, string and a few twigs etc.
I like Andy's file maker thing. Similar thing here.

Would a jawhorse take a heavy bashing with biggest mallet and big gouge on a lump of oak?

 

[eoinsgaff]

[/quote]I'm thinking of having a crack at a gnome.[/quote]

Human genome or garden gnome?

Excuse me, I couldn't resist.

 

[No skills]

Years ago I saw one of the triton ones demoed, it did seem fairly heavy duty. Hand sawing large pieces of wood, knocking in nails etc - there was a small amount of movement of the timber from what my fragile and unreliable memory tells me. I dont think youd break it easily but not sure how the mechanism would cope with odd shaped lumps of timber. I'd vision something with a nail or small point built into the jaw face to give a bit of a bite when the jaws clamped.

fwiw

 

[AndyT]

Yes, Jawhorse.

http://www.amazon.co.uk/s/?ie=UTF8&keyw ... vio6e3w3_b

I see that people who bought the jawhorse also bought this:

- is that what passes for a gnome down your way, Jacob? :lol:

 

[xy mosian]

'Cause if it were a really big lump you could carve as part of the tree ... then cut it off. Only joking. I like the idea shown in the link. I wonder if replacing the rope with a piece of timber would mean a smaller contact area and reduce the clamping force. Prehaps a wide rough web strapping?
xy

 

[Jacob]

..

I see that people who bought the jawhorse also bought this:

- is that what passes for a gnome down your way, Jacob? :lol:

Hmm. Very well done but would you want one on the edge of your pond? The goldfish would **** themselves!

They'd be happier with something like this