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Bar Clamps

This is where we don't want anything but evidence of your finest wood butchering in all its glorious, and photograph laden glory. Bring your finished products or WIP's, we love them all, so long as there's pictures, and plenty of 'em!

Re: Bar Clamps

Postby Dr.Al » 05 May 2021, 12:11

Dr.Al wrote:Pictures showing what the model looks like with short and tall jaws:

Image

Image

(Note there are some other changes to this model as I've been playing around with the end plate support - I'm still undecided as to whether the bar sits on the jaw bases or on one jaw base and an extended end plate)


and because parametric CAD is fun...

silly_tall_jaws.jpg
Daft Jaws
(24.76 KiB)


:lol: :lol: :lol: :lol:
Last edited by Dr.Al on 05 May 2021, 12:14, edited 1 time in total.
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Re: Bar Clamps

Postby Dr.Al » 05 May 2021, 12:12

droogs wrote:Allways thought he sounded a bit Sandwell and Dudley


I'm not sure exactly where he's from - I just remember a comment on one of his patreon threads saying his accent sounded like a cross between West Midlands and North-East Australia and the response from Neil Paskin was "spot on" or words to that effect.
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Re: Bar Clamps

Postby Dr.Al » 05 May 2021, 19:01

Image


The screw jaw is moved by a 150 mm long piece of M16 threaded rod. The plate on the back of the jaw (shown in isolation on the right-hand side of the image above) is held on the threaded rod by two clamping pieces. These are attached to the threaded rod but neither they nor the threaded rod is attached to the plate, so the threaded rod can rotate freely relative to the plate. Although it's not shown in the model, the hole through the plate is oversize (18 mm) and there's a reasonable amount of clearance between the clamping pieces and the plate so that the threaded rod doesn't have to be perfectly perpendicular to the plate or perfectly aligned with the centre of the hole.

In the original video, Neil Paskin made these clamping pieces by holding an M16 nut on a piece of threaded bar in the drill chuck and "turning" them with an angle grinder (and then cutting in half with a hacksaw). That's a perfectly reasonable approach, but I've got a lathe.

Image


This photo shows the set-up I used for turning the nuts to size: it's just a scrap bit of M16 threaded rod held tightly in the chuck with a washer to hold the nut away from the jaws. This isn't a good way of holding threaded rod as the jaws will damage the thread; I probably should have fitted my collet chuck and used that (as it would have given better concentricity of the gripped thread), but for this application I decided it probably didn't matter and this way was easier.

Image


This photo shows a sort-of before-and-after of the lathe work - some of the original nuts and some that have been turned.

Image


I probably could have used a parting tool to cut the nuts in half, but I decided to just do it with a hacksaw.

Image


While I was at it, I used the bandsaw to cut up the M16 threaded bar into 150 mm lengths; my home-made bandsaw cut-off table with its stop made this a very quick process.

Image


The finished clamp pieces are shown in this photo (along with the M16 threaded bar bits). The smooth (outer) side of each half-nut will be against the plate in the screw jaw. The rough hacksawed side will be facing out but the rough finish will disappear once I melt it with the TIG torch.
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Re: Bar Clamps

Postby 9fingers » 05 May 2021, 19:10

Last night I was idly wondering if it was worth having a thrust bearing on the moving jaw.
ebay was about £2.50 a pop but i did not get round to searching Banggood for a pack of 10 direct from China
Chinese bearings can be incredibly cheap for non critical applications.
You don't need quality or precision but might give a nice feel to your clamps.

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Re: Bar Clamps

Postby novocaine » 05 May 2021, 20:27

9fingers wrote:Last night I was idly wondering if it was worth having a thrust bearing on the moving jaw.
ebay was about £2.50 a pop but i did not get round to searching Banggood for a pack of 10 direct from China
Chinese bearings can be incredibly cheap for non critical applications.
You don't need quality or precision but might give a nice feel to your clamps.

Bob

I reckon youd get as nice a feel from a pair of conical washers.
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Re: Bar Clamps

Postby Dr.Al » 05 May 2021, 20:31

9fingers wrote:Last night I was idly wondering if it was worth having a thrust bearing on the moving jaw.
ebay was about £2.50 a pop but i did not get round to searching Banggood for a pack of 10 direct from China
Chinese bearings can be incredibly cheap for non critical applications.
You don't need quality or precision but might give a nice feel to your clamps.

Bob


That's a good thought (assuming the heat from welding the clamp plate doesn't bugger the bearing). I'll have a look around & see if I can find any cheap options.

Thanks!
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Re: Bar Clamps

Postby Dr.Al » 06 May 2021, 09:07

I've ordered some budget 51103 thrust bearings - £15 for ten (with a UK supplier, I could have got them for about £8 for ten from China but I went with the impatient option). They're 17 mm ID, 30 mm OD and 9 mm long so should fit quite neatly around the 16 mm threaded rod and against the 30 mm wide plate. I'll probably try one on the prototype to see what it's like & how easy it is to get the spacing tight enough for the bearing not to come apart but loose enough to allow for welding movement.

It's also going to make masking up for painting a complete pig, but I'll jump off that proverbial bridge when I get to it.

I suspect it'll be absolutely fine without the bearings (the movement is never going to be silky smooth with the welding tolerances associated with the sliding motion along the rail), but it might make the final tighten a bit smoother.

The bearings are rated for a static load of 21.2 kN and a maximum speed of 12,000 rpm, so that should be okay anyway :D
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Re: Bar Clamps

Postby AJB Temple » 06 May 2021, 14:38

Just as an aside, what thread do you think is optimal. I only ask because all my clamps are second hand. Some of them have a very fast thread that quickly closes the gap, others need a lot of turns. Prefer the former myself. Must be a deliberate design feature.
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Re: Bar Clamps

Postby spb » 06 May 2021, 14:40

Different tools for different jobs there - the finer threads will give (potentially) a lot more clamping force than the fast ones, at the expense of more time needed to set up.
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Re: Bar Clamps

Postby Dr.Al » 06 May 2021, 14:49

AJB Temple wrote:Just as an aside, what thread do you think is optimal. I only ask because all my clamps are second hand. Some of them have a very fast thread that quickly closes the gap, others need a lot of turns. Prefer the former myself. Must be a deliberate design feature.


I guess it depends on what you want out of it. A fine thread will give more mechanical advantage so in principle will give more force for a given torque. Having said that, the peaks and troughs will be shallower so the thread will be weaker. A coarse thread will move quicker and, for woodworking applications, will probably be fine.

One of the things I like about the bar clamp designs I'm making is it's (kind of) the best of both worlds. It uses a 2 mm pitch thread for clamping, which is relatively fine so gives plenty of force for a given amount of effort, but the sliding jaw can be moved in increments of 1.75 mm, so you never need to move the screw jaw very far. Obviously it would be better with a trapezoidal thread, but that would be a lot more expensive!
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Re: Bar Clamps

Postby AJB Temple » 06 May 2021, 15:12

Thanks. Makes sense. Struggling to think of a woodworking application where a great deal of clamping force is needed - presumably one can over do it and squeeze too much glue out. My old Record clamps can easily exert more force than I have ever needed, even with edge to edge gluing of boards.

It would be helpful at times if clamps were designed so that they can be linked together to make double the length.
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Re: Bar Clamps

Postby 9fingers » 06 May 2021, 15:18

AJB Temple wrote:Thanks. Makes sense. Struggling to think of a woodworking application where a great deal of clamping force is needed - presumably one can over do it and squeeze too much glue out. My old Record clamps can easily exert more force than I have ever needed, even with edge to edge gluing of boards.

It would be helpful at times if clamps were designed so that they can be linked together to make double the length.


many are designed with couplers in mind.
This is a bessey coupler
88DE50F5-779B-4109-BD17-4F69529DBE1C.jpeg
(244.07 KiB)

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Re: Bar Clamps

Postby Dr.Al » 06 May 2021, 15:38

AJB Temple wrote:Thanks. Makes sense. Struggling to think of a woodworking application where a great deal of clamping force is needed - presumably one can over do it and squeeze too much glue out. My old Record clamps can easily exert more force than I have ever needed, even with edge to edge gluing of boards.

It would be helpful at times if clamps were designed so that they can be linked together to make double the length.


The threaded ends of my bars should make it possible - I've had a few ideas about how to make some robust couplers (for all those times when I need to clamp lengths longer than 1.75 metres :lol: :lol: :lol: ).
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Re: Bar Clamps

Postby AJB Temple » 06 May 2021, 15:42

I've never seen those. I do have a dozen or so Bessey clamps in smaller and specialist sizes, but never come across those. Thank you.
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Re: Bar Clamps

Postby Dr.Al » 06 May 2021, 17:50

As I've decided to attach the ends to the bars with M12 screws instead of welding them on as Neil Paskin did, I have to include an M12 tapped hole in each end of the bars. There are a few ways I could have done this:

  • File two corners off an M12 nut, somehow hold it central in the end of the bar and weld into place.
  • Weld some steel into the end of the bar, then drill into the end (probably in the lathe) and tap M12.
  • Make some 20 mm square inserts with a central hole tapped M12.

The first option has the advantage that it doesn't need any special tools. The second option has the advantage that it makes sure that the tapped hole is central with respect to the box section. The third option is (I think) the quickest, so that's what I'm going with! I've got a 250 mm length of some finest grade skipium that happens to be the right size. I decided that the easiest approach was to cut this into 60 mm lengths then drill and tap each length using the lathe. The pieces could then be cut up into 10 mm lengths. I don't care too much about the finish on the face as I'm going to be welding over it anyway.

Image

This photo shows one of the 60 mm lengths after I've drilled it 10.5 mm and tapped it (with a spiral flute tap) M12 under power. After getting the first bar into the chuck and centred properly, I marked two of the jaws with a marker pen so I could just undo those two jaws, swap the bars over and tighten the same two jaws. This won't result in absolute precision of the hole in the centre of the bars, but it really doesn't need to be precise for this application.

Image

This photo shows three of the bars after they've been removed from the lathe chuck and one after it has been cut up into slices. The little vice on the left-hand side of the photo hasn't been used for a long time: I used to use it for holding stuff down on my mini-lathe when trying to do milling operations. Since getting my little milling machine, it hasn't been out much.

Image

For this operation the little vice was really useful for holding the short lengths of bar in the bandsaw vice so that they could be chopped up into little square nuts.

Image

This photo shows all of the resulting inserts. I need two per bar, so this is way more than I need for the eight clamps I'm planning to make, but I figured I might as well cut the whole bit of steel up and then I can keep the spares in case I want any other lengths in the future.
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Re: Bar Clamps

Postby Dr.Al » 07 May 2021, 16:58

The next job was to cut all the flat bar pieces to length (about 400 pieces in total as a result of making so many clamps in one go!). To help me keep track of things, I made a cutting list describing the size of each component (grouped by size of the bar from which they will be cut) along with the number of pieces required per clamp. If anyone feels inclined to make any of these clamps, let me know and I'm happy to send a copy of the cutting list with all the dimensions.

Image

Image

Most of these cuts were done with the jig shown in the second photo above. This was made out of an old bit of OSB (oriented strand board), a bit of hardboard (which, at 3.2 mm thick is very slightly thicker than the 3 mm flat bar) and a couple of fence jigs (shown in the first photo) that I'd previously made for cutting steel square with my metal-cutting circular saw (which is a lot nicer to use than an angle grinder, although an angle grinder would work fine - Neil Paskin used an angle grinder in his video). The right-hand end (in the photo) of the hardwood guide bar on both of these jigs was cut with the circular saw, so that end can be quickly lined up with a marked cut line; the saw runs along the plywood edge to make sure it cuts at 90°. However, for this jig that reference edge on the hardwood guide bar isn't used (although the guide bar itself helps keep the metal bar in place). I fixed the jig to the bottom plate with a couple of screws and used the saw to make a cut into the OSB and hardwood. I then measured from the far side of the kerf when placing stops for repeatable cuts.

Image

In use, a piece of steel is slid underneath the saw alignment jig up to one of the lines and then the saw is used (against the fence) to cut the part to length. None of the dimensions are especially critical in this project, but I clamped a bit of spare material at the end so that the flat bar could be slid up to a fixed stop for repeated cuts of the same length: this sped up the process considerably.

Image

The side pieces are a little more complicated in that they have an angled face. These were cut with two jigs: the one described at the top of this post and the one in this photo. The one shown in this photo makes an angled cut at the right distance from the (already square) end of the bar. The remaining piece is then inserted into the first jig (against a stop) and cut off square to make a second angled piece.

Image

This photo shows all of the parts that were cut up in this way. There are still about 30 more to pieces to cut: I was convinced I'd put all the bits of steel through the citric bath to remove the mill scale, but apparently I missed one. Ah well...
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Re: Bar Clamps

Postby Dr.Al » 08 May 2021, 17:23

Today was a bit of a bonus day: I had convinced myself I would achieve nothing today as most people I've spoken to have felt rough the day after their first AstraZeneca Covid jab, but I seem to have escaped without any ill effects, so I could spend the day in the workshop instead of bed!

I decided to weld the inserts into the bars first. The welds are relatively straightforward, but slightly awkward due to the length of the bars (and the relatively short length of my bench!)

Image

As the bars are too long for my metalwork bench, I decided to weld the inserts in with the bars held vertically. To support the bars for welding, I used a G-clamp to hold a welding square to the edge of my bench and then held each bar in place with a C-clamp. The advantage of the C-clamp (a wide jawed variant of a mole grip) here is that, once adjusted, it's very quick to unclamp one bar and clamp up the next.

Image

Image

One disadvantage of having the bars held vertically is that it means that I'm working a long way off the bench. To make this more comfortable, I used my welding arm support with an extra bit of aluminium extrusion attached to the end. For the really long bars, I held them diagonally, but using the same welding square to support them.

Image

Image

The other disadvantage of vertical bars is that there's a risk of the insert falling down into the bar. To stop this from happening, I cross-drilled an offcut of M12 threaded rod and inserted a roll-pin. This can be inserted into the threaded insert and dropped into the end: the roll-pin stops the insert from falling. The insert can then be tack-welded in place, the threaded rod removed and the welding completed. I made sure I placed the tack welds close to the roll-pin but on the side that is clockwise to the threaded rod. That meant that, as the threaded rod was turned anticlockwise to remove it, the roll-pin had risen up as far as possible to give it the best chance of clearing any bulge caused by the tack welds.

Image

Image

I'm not sure if this step was really necessary, but I decided to clean up the end faces of the bars. I did this on the milling machine as I have one and it seemed easy, although there are plenty of other approaches I could have used (or I could have just not bothered). The advantage of doing this is that it gives a nice flat surface for the end plate to bear on when the screw is tightened.
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Re: Bar Clamps

Postby Dr.Al » 08 May 2021, 17:24

Image

Image

The next job was to weld one half of each split M16 nut onto the end of a bit of threaded bar. The other half will be welded in place after passing through the hole in the rear plate of the screw jaw, but I thought I'd get this one done in advance.

Image

The first welding job for the sliding jaws is to fix half an M12 nut onto a piece of 3 mm × 31 mm × 50 mm steel bar. The nut (which was cut in half with a hacksaw after coming out of the citric acid bath) needs to be at the end of the flat bar and (more importantly) needs to be aligned with the flat bar.

Image

Image

The photos above show the jig I made to help with this process. It was made out of various offcuts I had lying around, hence the slightly strange sizes of pieces. The base plate is aluminium, the thin flat bar pieces are offcuts of 3 mm steel and the "wings" that support the side of the nut are aluminium. It's held together with double-sided tape.

Image

This photo shows how it is used. The piece of flat bar gets slid into the jig as far as it will go (it slides easily as the spacer pieces are the same thickness and there's the additional thickness from the double-sided tape). A half-nut is placed in the pocket and an offcut of M12 threaded rod dropped into both half-nuts. This makes sure that the half-nut is aligned with the axis of the flat bar. My welder's third hand holds the threaded bar down and the half-nut can be tack-welded in place. It's then removed from the jig and fully welded.

Image

With the jig made, I was able to tack weld all of the pieces in about 20 minutes and be confident that they were all in the right place. I did have to be careful to ensure I didn't melt the thread at all as there's no way I can pass a tap through the thread to clean it up if I get it wrong!
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Re: Bar Clamps

Postby Mike G » 09 May 2021, 08:24

That's really neat and thorough work, Dr Al.
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Re: Bar Clamps

Postby 9fingers » 09 May 2021, 08:38

I’m confused dr al
I get the m12 half nut bit but this
“The next job was to weld one half of each split M16 nut onto the end of a bit of threaded bar. The other half will be welded in place after passing through the hole in the rear plate of the screw jaw, but I thought I'd get this one done in advance.”
Eludes me and also I could not see it on your cad model.
Fascinating thread!
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Re: Bar Clamps

Postby Dr.Al » 09 May 2021, 09:01

9fingers wrote:I’m confused dr al
I get the m12 half nut bit but this
“The next job was to weld one half of each split M16 nut onto the end of a bit of threaded bar. The other half will be welded in place after passing through the hole in the rear plate of the screw jaw, but I thought I'd get this one done in advance.”
Eludes me and also I could not see it on your cad model.
Fascinating thread!
Bob


Glad you're enjoying the thread. The CAD model doesn't make it especially clear, but you can see the parts in this image (which has lots of the other bits removed):

Image

and this image (which is a cross-section with all the bits visible):

Image

The threaded rod (grey block near the top-left of the cross-section) goes through a nut on the end plate. It then passes through the back plate of the screw jaw (green plate in the top image) with half a rounded-off M16 nut either side of the plate (one shown green, one shown grey). The half nuts are welded to the threaded rod, but nothing is welded to the plate. The idea is that the threaded rod can spin freely in the plate but will push and pull the plate back and forth as you turn the threaded rod in the end plate's nut.

The one I've welded in place so far is the one shown in grey in the images above.

You can see Neil's version 3 minutes into the video: https://youtu.be/P0wLjQqf-zM?t=180

This part of the assembly is where the thrust bearing you suggested might go, something like this:

barclamps_model_screw_jaw_with_thrust_bearing.jpg
(38.11 KiB)


Does that make sense?
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Re: Bar Clamps

Postby 9fingers » 09 May 2021, 10:32

OK Gotcha!
A mix up on the subtleties of split nut Vs half nut. The text relating to the "threaded round bushes" you call split nuts, were next to a photo of hex nuts cut across their diameter.

I am enjoying the thread and almost want to start making some myself even though I've got a tolerable selection of bar and pipe clamps.
I do have about half dozen sash cramps in various states of disrepair/parts missing so might get my hot metal glue out and make the parts needed to make them usable.

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Re: Bar Clamps

Postby Dr.Al » 09 May 2021, 14:22

9fingers wrote:OK Gotcha!
A mix up on the subtleties of split nut Vs half nut. The text relating to the "threaded round bushes" you call split nuts, were next to a photo of hex nuts cut across their diameter.


Ah, good point - I'd started calling them "split nuts" to distinguish them from the half nuts, but maybe it's not that clear.
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Re: Bar Clamps

Postby 9fingers » 09 May 2021, 14:34

Dr.Al wrote:
9fingers wrote:OK Gotcha!
A mix up on the subtleties of split nut Vs half nut. The text relating to the "threaded round bushes" you call split nuts, were next to a photo of hex nuts cut across their diameter.


Ah, good point - I'd started calling them "split nuts" to distinguish them from the half nuts, but maybe it's not that clear.


Even the engineering fraternity cause confusion over nut nomenclature.
To a fixings supplier a half nut is a thinner than standard nut (aka a full nut). However the split nut used to disengage a lathe leadscrew is commonly known as a half nut too.

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Re: Bar Clamps

Postby Dr.Al » 09 May 2021, 14:40

I started today by cutting up all the remaining bits of bar and some short lengths of 25 mm × 25 mm × 2 mm box section that sit inside the sliding jaw.

Image

The pieces shown in blue in this image are shown as two single pieces, 6 mm × 15 mm × 50 mm. As I'm making everything else out of 3 mm flat bar stock, I'm making each of these out of two pieces, each 3 mm × 15 mm × 50 mm. The chamfer you can see at the top of each part is to give clearance for the weld beads attaching the M12 threaded rod to the box section bar.

Image

On the prototype, I cut this chamfer using a hand file, but given I've got rather a lot of them to do, I decided it would be quicker and easier to use this little chamfering end mill I picked up at the Bristol Model Engineering Exhibition a few years ago. With the home-made X-axis power feed on my milling machine, this dealt with all the chamfers very quickly.

Image

Image

Image

While I was on the milling machine, I decided to drill all the holes in the various plates (the first photo is the hole in the end cap, the second is the hole in the rear of the screw jaw through which the threaded rod passes and the third photo is the end plate with one hole to attach it to the bar and one hole for the M16 threaded rod to go through). On the prototype I drilled these holes on the drill press, but the milling machine is much more capable and the X-Y table combined with the stop (for repeatable positioning of parts in the vice) makes it easy to get the holes in about the right place. None of the hole locations are that critical: they're deliberately oversized (14 mm for 12 mm screws and 18 mm for the M16 threaded rod) to allow for parts moving when welding.

The only thing that made the process a bit more awkward was that the quill return spring on my milling machine snapped part way through the process:

Image

Thankfully it didn't stop me from doing the drilling, I just had to return it to the top by hand and then lock the quill up after each operation. Spare springs seem to be readily available and not too expensive, so that's a relief!
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