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Precision table saw fence

Discussion in 'General Talk' started by Matt Roberts, Jun 10, 2015.

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  1. Matt Roberts

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    Hi all, hopefully some of you experts can give me a steer on this.

    I'm looking to create a precision table saw fence for a home-made table saw.

    So what I effectively need are two rails, with a straight edge sliding perpendicular to the two rails. I've been looking into using the V Slot rails along with either Vwheels or possibly even T slot nuts to allow the fence (another piece of V slot extrusion) to slide across - pretty much the same as any standard CNC build I've seen. Same sort of principle as this image:

    [​IMG]

    There are obviously a few issues to consider:

    1. The perpendicular fence needs to remain at perfect right angles to the rails as it slides across the whole length of the rails - I'm concerned that by using either the VWheels or T Slot nuts will have a small amount of play in them at either end which will either cause the fence to stick or will mean one end is millimeters out from the other
    2. The fence needs to be locked into position - I'm less concerned about this, as I can fashion a cam lever to clamp it locked
    3. Once locked, the fence needs to be rock solid. As I push the wood against it and run it through the saw, there will be a fair bit of pressure against it
    Without buying all the parts to test, can anyone give me an idea if using V Slot extrusions and either wheels or T Nuts sounds feasible?

    Thanks very much for any help & advice!
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    T-slot nuts are definitely out as there is way too much play in them. Wheels are probably workable but in the end, the amount of play you will have at the far end is in direct proportion to how widely spaced the wheels are at the near end. The size and stiffness of the extrusions will also have an impact. A suggestion would be to incorporate TR8*8 screws both front and rear with pulleys at one end and a continuous belt between them to keep the system in sync. This would not only provide an effective method of locking both front and rear at the same time but with a properly marked dial on a crank wheel, would allow for metering precision adjustments of the fence.
     
  3. Matt Roberts

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    Thanks very much for the reply. So you're suggesting using the threaded rod to effectively make a large clamp? Sounds like a good idea, but might take a while to move large distances - I'm looking for a range of 80cm from the blade to the edge of the table.

    Would v wheels on longer plates at the top and bottom not provide enough horizontal stability if the fence was bolted at right angles to the plates? Or could I use v wheels on either side of the extrusion rail perhaps to 'clamp' the plates to it?
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    The problem as to whether something works or not is that there is often a very substantial gap between "should" and "will". While what you are suggesting "should" work, as I haven't specifically tried it I can't specifically say that it will. You are counting on the stiffness of the overall system to keep it in alignment. The only way to know if something like this will work is to give it a try and see if the results meet your expectations.

    Beyond that, the only way to say that a system "will" work without trial and error is to tie the two ends into a system that won't allow misalignment. The screw suggestion above is such a system. Others would include the looped belt system that is popular with the 3d printer group or a wiring system akin to a Mayline parallel bar. Unfortunately I'm not in a position at the moment where I can detail either of those out.

    So best suggestion at the moment would be to give what you are thinking a try and see if it works. If it doesn't, there's generally no loss involved as one of the beauties of V-slot is how easily parts can be shuffled from one concept to another.

    BTW on the screw system, you'll find with the TR8*8 screws that once the screw blocks have worn in a bit you won't need to use the cranks to move them. You just grab on and pull and due to the steep angle of the threads, the screws will spin on their own inside the blocks.
     
  5. Dave Millard

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    Are you not trying to solve the problem in the wrong way?

    A typical Beisemeyer table saw fence isnot perfectly square as it moves across the table. It is the act of locking it, which squeezes the fence against a surface that is perpendicular to the blade that straightens it. The secret is in the locking mechanism.

    Even the most expensive table saws have a relatively primitive runner for the fence on the outfeed side. V Slot will make a nice fence if it is straight, look elsewhere in this forum for some who have had experiences with very slightly bowed V Slot.

    You may want to look at the Incra Table Saw fence for inspiration if you want to run on wheels.
     
  6. Matt Roberts

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    Thanks Rick & Dave, you've both been very helpful.

    Dave, you make a really good point - but I'm guessing the locking mechanism I had in mind would never be as solid as a proper cam lever on a machined fence.

    I get the feeling that I'm trying to achieve too much - there's a reason why proper manufactured fences exist - they give you the precision that home-made ones lack.

    Thanks again for the advice!
     
  7. d_banduk

    d_banduk Well-Known
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    The timing of this thread is impeccable! I'm fairly new to Openbuilds and took the plunge during the free shipping weekend to order (almost) all the parts for my table saw fence. They arrived here in the UK a couple of days ago and I just got them home today. I have it half built already just waiting for a couple of additional parts and I'll be able to finish the build post and upload some pictures. I'm using 40*40*1500 for the rails front and back and 40*40*1000mm for the fence with almost identical cart and locking setup to Mark's Mitre Saw Stop. I've built carts for both rails.

    So far this thing is solid and straight, there is no visible flex in the 40*40 even when I only had the first 300mm of a 1500mm length supported. The clamp for the locking mechanism is what I'm waiting on but with wheels at either end of the cart and the clamp applying pressure in the middle I'm expecting a similar affect to what you get with a commercial version. I might end up replacing the pad on the clamp with a longer 'shoe' to apply more friction without increasing pressure just to keep any bending to an absolute minimum but maintain a good lock. I've used X-treme solid wheels and I've got no play in the carts.

    I'm no pro, I've had my table saw just over a year and it's a hobby saw built in to a custom bench so might not be exactly what you're looking for but I hope my experience with it will help. A commercially made fence might perform better but when you offset the cost of those things against what you might lose in accuracy I think you've just got to try and make your own. Particularly for someone like me who isn't a professional. Having got this half built I'm already confident it's going to be great and it's screaming out for some additions and jigs already.

    I'll see how it goes and let you guys know! Don't you just love playing guinea pig!
     
  8. Matt Roberts

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    Sounds really good - I'm pleased it seems to be working out!

    Really looking forward to seeing pictures of the build - keep us posted!

    Cheers
     
  9. JustinTime

    JustinTime Master
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    @d_banduk, can you post some pics so that we can admire your work? And maybe go OOHH and AHH! :)
     
  10. Ryan James

    Ryan James Well-Known
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    Another option, one that I haven't seen with v-slot specifically, are linear bearing pads made of UHMW. The fence would ride in the slot and should not have a lot (if any) play. I've only the seen the system for standard t-slot extrusion, though.
     
  11. d_banduk

    d_banduk Well-Known
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    Prototype No.1

    So here goes. I've been at work all day but couldn't resist trying to get this thing at least to a point where I can test the theory. I did, but, and isn't there always a but, (as I'm sure you can tell by my witty title here) there are problems to solve and I have to admit I love solving a good problem. So here's what she looks like:

    20150701_213536.jpg

    Here's what I put together to join the fence to the cart, please bear in mind this is just a mock-up and is what I could fashion in the time/brain capacity I had at the end of a long day. This will not be the final setup:
    20150701_213335.jpg
    And from beneath:
    20150701_213324.jpg

    So after the OOOHs and AAHHs here's the deal. I plan to redesign the plywood part, lets call it the tee bracket, yeah that sounds good. It's 12mm thick. It works well but is poorly positioned and I think it can be more compact and if I get it right I would like to remove the front one completely. I've got some scrap of this so will probably try a couple of different shapes before I settle on a good one. The securing points will also be countersunk and this quick mockup means the fence can only be used on the left without flipping the whole assembly. As part of that change the clamp will get moved, it's right in the way of loading the saw but I just wanted to see if it worked. It will also get a bigger handle!

    Here's what's works well:
    1. The profile itself is perfect I have no worries about it's suitability for this job.
    2. The carts work great, no problems there. No play etc. Just for notes, I've put 4 eccentric spacers on the front cart to enable mincro adjustments to square as necessary down the line with out having to detach anything. Youonly have to loosen the attachment to the rear cart.
    3. Adding the fence to the rails has actually stabilised the rails. See those flimsy flat steel brackets I'm using to support the rails (they're temporary too) they obviously flex and I've currently only got 2 of them supporting the first 300mm or so of each rail but adding the fence has actually stiffened the whole assembly up.
    4. The rubber stop on the clamp grips the aluminium really well. even with minimal clamp pressure trying to make it slide along the rail takes far more horizontal pressure than I would ever put on it during a cut.
    Here's what's not so good. Suggestions please:
    1. I've run out of tee nuts! PPPPPP
    2. The fence moves under pressure at the points where it attaches to the tee brackets. The two points secured from below. This is down to and limited by the play in the tee nuts. One option would be to drill and tap the profile inside the slot (would rather not). I've already reduced this significantly by flipping the tee nuts so that the raised part sits in the slot. With 2 more securing points I think this will be sorted, if not then replacement with the drop in tee nuts with serrated edges. Certainly worth trying before the drill gets fired up.
    3. This is the big one. The clamp flexes horizontally. The rubber stop holds fine and the action is great but the clamp mechanism itself has enough play in it to move from side to side. I haven't measured it because it's clearly enough to be a show stopper. This thing is small and cheap and not designed for lateral motion so the best I can do tomorrow is hammer the rivets that hold it together to try and tighten it up a bit but it's also made out of the same stuff my flexy support brackets are so it might help but is not a final solution. If anyone has some experience with these and knows a brand that make very robust but small ones I'd be grateful to hear. It's a real shame because this design of mechanism is perfect for the job but it's just not playing nice.
     
    Knut Bøje likes this.
  12. d_banduk

    d_banduk Well-Known
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    @Ryan James This was what I first looked into when I decided extrusions were great material for a fence. I ruled them out for two reasons, firstly I found it really difficult to find a source for them in the UK and secondly from what I could find overseas they are pretty pricey for what they are.

    This one is $45 from 8020 and they don't ship outside the US.
    Hutch here has made a fence with it. Looks pretty good.
    There's another for a bandsaw here.
     
  13. Ryan James

    Ryan James Well-Known
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    Hutch's is the one I saw. I've thought about trying to do the same thing you have. Locking it down is the difficult part. I've wondered if a bolt that locks down with a t-nut to the extrusion wouldn't work better than the clamp.

    As for mounting the horizontal rail, it might be better to drill through the lower track and attach with some bolts to the table. It seems like it would give it more strength.
     
  14. Knut Bøje

    Knut Bøje Well-Known
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  15. JustinTime

    JustinTime Master
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