Saturday, August 23, 2008

Getting To Know Roubo-Part 3



After a few more weeks of one-on-one time with the Roubo bench, one thing that I didn't catch in the design phase is rearing its ugly head. The parallel guide on the sliding vise renders the shelf completely useless for all but the thinnest "stuff". Right now I have a sticking board, a sanding board (for fitting oud ribs) and shooting board living down there. Anything thicker and the sliding vise doesn't do much sliding. It becomes a couch-potato vise. I can fix this problem quite easily by simply removing the shelf. The up side is it won't end up being a giant tool tray (in other words a junk collector). The downside is I loose some handy storage space for bench accessories, and the shelf really is the best place for those. So as I suspected I would, I'm now in the planning stages for retrofitting a St. Peter's Cross on the sliding vise. I'm going to build a prototype before I start retrofitting the sliding vise.

17 comments:

  1. Thanks for the updates! It's very helpful to hear your thoughts.

    As for shelf space, what if you moved the shelf up? (Or built another one higher). The screw from the sliding vise would prevent storing anything too large, but it seems like there'd be some useful space if the shelf were just above the parallel guide.

    Just a thought...
    Andy

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  2. Andy,

    Building the shelf higher would require fitting a rather long rail between the legs. It's an interesting idea to consider. If I had a bigger shop I'd just remove the shelf altogether and store my bench accessories along a wall or somewhere else. I think if I can get the St. Peter's Cross built with success, it will be the best solution. And I know of quite a few people that would benefit from someone doing the groundwork on developing a functional vise like this. I have a few people to help along the way too, so hopefully the result will be very good.

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  3. Hi, I read your thread in other forums where you were reporting your St-Peter's cross prototyping. You were indicating instability when opening wide the jaws... I am considering building such a vise this winter and I plan on prototyping with the fixed pivots for the cross members being at the bottom of the leg instead of at the top just below the screw... I would like to have other's input on this idea? I thought it would help with stability since it makes the distance between the pivot and the screw as long as possible all along the travel of the jaws...

    I love your blog, and your bench even more!

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  4. That's an interesting idea about placing the fixed points of the X at the bottom. I'm not quite picturing how it makes a difference though. Can you elaborate?

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  5. The problem I want to addess is that the wider the jaws are opened, the slightest play in the sliding mechanism is amplified. Other leg vises such as one with screws or dowel plates have the parallel mechanism as far as possible from the screw. I am then questioning the St-Peter's cross diagram with the fixed pivots being close to the screw. If we transfer the play in the sliding mechanism into degrees out of parallel for the jaws, there would be more degree resulting in the parallel mechanism being closer to the screw than for being farther from the screw(this for the same amount of play in the sliding mechanism) thus providing less stability to the vise.
    Just an idea, may not be worth the trouble, I will at least give it a try when I get to my bench project in a few months.
    Regards
    St├ęphan

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  6. I look forward to hearing about your vise support prototype, especially the size of the parts required to support firmly the vise in a parallel position. I think the cross would be an ideal solution if it was strong enough to maintain the vise bottom under high clamping pressures. However, if you're only supporting work on the sliding vise, such pressures might not be necessary so you could get away with more.

    I would be very interested in your thoughts for using this in the leg vise position.

    I'm very thankful for your blog on your Roubo bench. I've also admired the 18th Century Roubo bench from Landis' book for many years (not the German version like yours though). The dovetailed tenons are unique and beautiful. I am also thankful for Schwarz's contribution, however it seems my plans for trying to build a unique bench will no longer be unique (especially if they're being marketed now). But in the long run this is probably more benefitial for me than I can appreciate. I love the fact you can continue to modify and enhance your bench too. A piece of beauty with continued challenges. Thanks again!

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  7. Stephan,

    Thanks for your thoughts on the mechanism. One idea I'm toying with is using two wheels on the moving portion of the X, mounted on eccentric shafts, so the distance of the sliding ends can be adjusted. A spring plunger with detents is a possibility too for quick adjustments when opening the jaws wide, if needed. Of course this will all be worked out with a prototype, which I've already started. Stay tuned.

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  8. Theodor,

    The main reason I'm pursuing the X vise is to free up my shelf. I'm not interested in it for the stationary vise, since I really like my skateboard wheel equipped parallel guide, and it's overall simplicity. Yeah, moving the pivot pin is a small issue, but it doesn't bother me. The wheels make this vise effortless to operate, and I doubt that the X vise will ever be as smooth, since the chop must support it's own weight. I'll trade smoothness for my shelf though. Thanks for dropping a line.

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  9. Hi Jameel,

    They say that imitation is the sincerest form of flattery. I have been so amazed by your German Roubo that I decided to build one myself. I hope you don't mind that I intend to use your design. I purchased a bench crafted tail vise and am waiting for delivery. (I even have a bag of skate board rollers waiting in a drawer)

    Now for the interesting part. I agree with you that the Croix du St. Pierre may be a great solution for the sliding leg vise. I saw the picture in Landis' workbench book. But, it was mentioned in the text that the vise had some slop in it. So, I have been looking for a design that I know will be robust and tight enough.

    Now, unless you and your machinist friend have already devised a solution, I think I may have found something that might work.

    Check out this link. It is for a Motorcycle Scissor Stand. Let me know what you think. I think this can be easily modified and installed to do the trick.

    All the best,

    Cosmo


    http://www.northerntooluk.com/products.asp?partno=1803764E&cm_mmc=Affiliate%20Window-_-Datafeed-_-AW-59235-_-Product-1803764E&cm_mmc=Affiliate%20Window-_-Appended%20Click-_-AW-59235-_-null

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  10. Cosmo,

    First, thanks for the vise order. I think you're going to love it. Secondly, I'm flattered that you're building a bench like mine. I wish you good success for the build, and a bottle of pain reliever. You'll need it!

    That motorcycle stand obviously uses the same principle as the X-brace vise (St. Peter Cross). My only concern is that you'll be stuck trying to build your vise around the lift, instead of the other way around. I'm still prototyping my version, but it will be sized for typical bench use, and thoroughly tested before we offer it. Drop me an email when you get your bench finished. I'd love to see it.

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  11. Jameel,

    Great. I guess I will wait unti you figure it out. Hopefully, I will simply be able to order it from you!

    I assume you intent to design it around your existing sliding vise?

    Also, I understand what Stephan (above) was saying about slight looseness in the mechanism translating into a bigger slop issue.

    I think one way around that would be to have TANDEM crosses. When we think of ST.PX we think of one X. I have seen a configuration with 2 vertically aligned crosses. Which to me seemed like it would be more robust.

    C.

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  12. Jameel,

    You've got another fan! I am very impressed by your ingenuity and craftmanship. I've ordered two wooden screws and a Benchcrafted vise (nice work), and I've got my order of southern yellow pine placed at my northern Maine lumberyard. I may have a simpler solution for the parallel guide. What if you built the sliding vise longer so that the parallel guide moves back and forth BELOW the shelf? This would involve moving the v-groove back slightly, say 1 inch, from the plane of the legs. Then attach a 1-inch thick board to the front of the sliding portion to bring the face flush. This board would extend down to about 1 inch off the floor. The parallel guide would go through this board underneath the shelf. You would have to space the guide far enough below the shelf to allow clearance when removing the whole vise. Do you think this thickness would be enough to take the pressure of the steel pin when the vise is cranked down? I'd appreciate your thoughts before I start cutting wood. And thanks for the super informative blog!

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  13. Sean,

    Glad you are getting something valuable from the blog. And thanks for the vise order too! You're on your way to a fantastic bench.

    About the parallel guide on the sliding vise. That's an interesting idea. I'm not sure that 1" would be beefy enough to withstand the pressure over time. This would also necessitate moving the front rail back by the thickness of the outer chop (1" as you mentioned). I think having the bottom rail in plane with the legs and front of the bench is important. I wouldn't want to give up this aspect. Of course the ultimate solution is an X-brace or St' Peter's Cross, which we're developing. I doubt we'll have anything ready by the time you build your bench, but it should be an easy retrofit once we get it nailed down.

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  14. Maybe I'll try beefing up the front chop with some steel to give it more rigidity. I'm curious as to why having the front rail in plane with the top and the legs is critical. A wide piece would be clamped between the two vises which should handle torsional forces. I can imagine clamping a narrower, long board vertically in the one leg vise without the extra support of the rail below might cause difficulty? The St. Peter's cross will be an elegant fix, but I don't want to wait that long! :-)

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  15. It provides extra support for holding long boards vertically, as you point out. I'd have to try your idea in context though to offer a better opinion. Thinking it out is a great way to work out problems though. I don't blame you about being impatient. If we do produce the X-vise, it should be retrofittable. (is that a word?!)

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  16. Jameel, just wanted to say thanks for all the detail in your bench blog. Your insight and, ultimately, the products that have come from that insight are awesome. I'm hoping to duplicate your bench in the coming months.

    Is there anything new with the development of the St. Peter's Cross? Perhaps not with the release of the Glide. I don't think my budget will allow for two Glides so I'm currently thinking the tail vise and two wood screws as in your original Roubo.

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  17. Thanks Dave. I'm still developing the X-guide for the leg vise. Look for a blog post soon about my impressions of the bench after using it for the past year.

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