Bar Clamps

[bricol]

I fitted a 15 quid Peugeot 106 boot gas spring (300mm travel) to my mini mill and threw away the original sprung assembly.

 

[Dr.Al]

I fitted a 15 quid Peugeot 106 boot gas spring (300mm travel) to my mini mill and threw away the original sprung assembly.

Interesting. Any particular reason? The spring assembly has always seemed to work okay on mine.

 

[Dr.Al]

This afternoon I started work on tack welding the frames together. It's amazing how long everything takes when you have to multiply each job by 10! The photos above show the jig I used to attach the first side to the base of the sliding jaw. It's based on an aluminium fixture plate I made a few years ago. The fixture plate has holes (alternately reamed 8 mm and tapped M8) on a 20 mm grid, so I attached a couple of 20-40-80 blocks to use as reference edges. An eccentric screw clamps the base into place and then a spring clamp holds the side of the frame in place to make it easier to attach the cantilever clamp to hold it more firmly.

For now I just did a couple of tack welds along the bottom edge to join the pieces together.

For the screw jaws, I used the same fixture, but put the small ledge pieces in at the same time. I had to use a different spacer between the base plate and the eccentric screw as the base plates are a bit narrower on the screw jaw. The plate is intended to be 3 mm × 31 mm × 50 mm, but I ran out of 50 mm wide plate so I made these out of 30 mm plate - hence they're 3 mm × 30 mm × 50 mm. The difference shouldn't matter as it just means there's a gap on the outer edge on one side: that gap can be filled up with a weld bead. The bottom two tacks in the second photo were done with filler rod to make a decent joint; the top two were done without filler to minimise the size of the weld: ideally I want these welds to sit within the radius of the box section that will slide along here.

After tacking the pieces together, I took the spring clamp off and welded the spacers together and to the frame on one end. I did this without filler, just because it was quick and easy to do so. Amazingly I didn't melt my 20-40-80 block when welding any of the frames!

This photo shows what it all looked like with one side of each frame tacked in place.

These two bits of wood were the "jigs" I used to complete the frames. They started out as one piece of oak that I hand-planed down to 25.5 mm thick. I then separated and shaped the two pieces. One is a 25.5 mm rectangular prism with one chamfered edge; the other has a ledge on one side and a scrap of pine nailed to the other side to help with assembly. When I made the prototype, I spent ages worrying about what angle to use for the sliding jaw assembly. In the end I realised it really doesn't matter that much - there's plenty of opportunity to tweak it after welding it together (filing the back to get it to sit horizontally and lowering the jaw piece to get the right drop height).

This photo shows how the jig helps with assembly. In practice, I don't fit the internal bit of box section until the frame sides are clamped together (it's thinner than the wood so can easily be slid into place), but I thought it helped for the photo. The box section will be ground down to match the width of the frame after everything is welded together.

I used a C-clamp to hold the frame together to weld it. The box section is only held in by gravity here, but that's good enough to get some tack welds on the corners.

This is what a sliding jaw looks like after tack-welding it together. At this point the C-clamp can be removed and the wood "persuaded" to come out by tapping it with a hammer. I'll come back to doing some proper welds later.

The screw jaw "jig" has a chamfer on one corner. That's there just to make sure it clears the tack welds on the frame and is about the same size as the radius on the corner of the box section it's emulating.

This shows the "jig" for the screw jaw frame being used. It's simply a spacer that ensures that the box section will slide easily through this bit of the screw jaw. The top plate is a lot lighter than the box section used for the sliding jaw, so I held it down with my welder's third hand.

This shows all the frames having been tack-welded together.

The last bit of preparation welding was to attach the other pair of ledge pieces to the screw jaws. Like the first ones, I did this without filler rod for speed and ease. They were held in place with spring clamps, so were quick to put together and doing all ten screw jaws took very little time.

This photo shows the jaw frames with the second set of spacers added.

That's it for today; I'll have to go back and finish welding all of the frames properly (rather than just having tack-welds everywhere), but I thought it was time to call it a day.

 

[bricol]

Interesting. Any particular reason? The spring assembly has always seemed to work okay on mine.

More consistent - and I wanted the room to mount the scale for a DRO.

Lovely, smooth action now - with a damped section at the top of the travel. A lot cheaper than buying an industrial gas spring.

 

[Dr.Al]

More consistent - and I wanted the room to mount the scale for a DRO.

Lovely, smooth action now - with a damped section at the top of the travel. A lot cheaper than buying an industrial gas spring.

Have you got any photos you could share?

 

[Dr.Al]

The next job was to finish the welding on all the frames. With everything tack-welded in place, this was a relatively quick process. Having said that, with twenty frames to tack, it still took almost two hours of pretty much constant welding (I didn't even lift my helmet visor once in that two hours!)

When Neil Paskin made his clamps, he drilled a series of holes in the sides of the frames so that he could plug-weld through the holes to join the side pieces to the inner pieces. When I made the prototype, I did the same thing, but having made it I decided that access through the top was good enough that I could make a good enough joint without having to bother drilling all those holes.

Once the frames had cooled down, I took advantage of the fact that the sun was shining and took the sliding jaws outside to grind off the excess box section with a 40 grit flap wheel in an angle grinder. I then gave the sides a quick once-over with an 80 grit flap wheel.

 

[My Old Landy]

I really enjoy your build threads, you have a lot of skill. They are an inspiration to me!

 

[Dr.Al]

I really enjoy your build threads, you have a lot of skill. They are an inspiration to me!

Thank you! It's nice to know the write-ups are appreciated. I don't feel like I have a lot of skill: I feel like I'm stumbling in the dark & hoping for the best most of the time!

 

[My Old Landy]

Thank you! It's nice to know the write-ups are appreciated. I don't feel like I have a lot of skill: I feel like I'm stumbling in the dark & hoping for the best most of the time!

You hide it well my friend

 

[Dr.Al]

You hide it well my friend

Just wait until I get onto the painting stage

 

[selectedgrub]

I really enjoy your build threads, you have a lot of skill. They are an inspiration to me!

Snap. I was just posting about this.
A big thanks for sharing.

 

[Dr.Al]

Snap. I was just posting about this.
A big thanks for sharing.

Thanks @selectedgrub

 

[Dr.Al]

Before carrying on with any welding, I did some testing of the fit of all the jaw frames on the prototype bar (I haven't welded the threaded rod to the final bars yet). The aim of this was to check two things:

1. The jaw frames should move freely along the whole length of the bar.
2. In the case of the sliding jaw, the jaw should sit parallel with the bar when the half-nut is engaged with the thread. If it sits with the rear edge high, a small amount can be filed off the lowest edge of the short bit of box section welded into the frame to sort this out. If it sits with the rear edge low, the rear face plate for the jaw can be mounted a little lower than the box section to sort it out.

This didn't go well...

None of the screw jaw frames would slide on to the box section (even with a bit of box section that didn't have the threaded rod attached, so it wasn't due to the ledges being too wide). Somehow, the side plates had ended up slightly too close together, not leaving enough clearance for the box section to run smoothly through. I don't really understand why this happened as the "jig" (bit of wood) I used was the same one I used on the prototype and that worked fine. The only vague idea I've had is that the heat of welding the prototype caused the wood to shrink by enough to make a difference. The frame sides looked to be parallel (and needed a fairly even amount taking off the side of the frames), so it's not as if they've bent inwards at one end and closed up because of that. Also weirdly, the sliding jaw frames (which used a jig cut from the same piece of wood - after planing to size) slid on the box section perfectly.

Anyway, at least it was solvable, it just made me very grateful to have this little "power file". I'm not sure what I'd do differently if I made them again; although checking the frames after tack-welding would have given me a chance to fix the problem more easily.

The second check involved checking that the sliding jaws sat parallel with the bar when the half-nut is engaged with the thread. Six of the jaw frames were absolutely spot on. Three of them tilted forward a bit (of which one had another problem) and one tilted back a little. The one that tilted back didn't really need anything doing to it: when the back piece is fitted it can be fitted a little lower than the bottom of the box section and it will support the frame.

For the three that tilted forward a bit, I had to file down the rear corner of the angled box section piece. As the angle of the box section is quite steep, there wasn't much material that had to be removed and I just did this with a hand file.

One of those three had another problem that had to be sorted first. Somehow, its nut had ended up off-centre. I've no idea how that happened. Maybe it was the last one I welded and the double-sided tape I'd used to hold the jig together had started to perish, but I'm really not sure. Bearing in mind that I'm making 10 frames with the aim of getting 8 good ones, I seriously considered just chucking it in the bin and forgetting it, but in the end I got the Dremel out and cut the nut out.

I could then use the prototype bar as an alignment jig and was able to tack the nut in place. I then removed the bar and welded all the way along the front edge and (with the TIG torch plunged deep inside the frame and pretty much out of sight) I also managed to get a couple of tack welds on the back the of the nut.

 

[Dr.Al]

With all the jaw frames sorted, I could get on with welding. I started by fitting all the back plates. Note that, in the case of the screw jaw, this is a different sequence to the one used by Neil Paskin - he attached the M16 threaded rod to the plate before welding it into the screw jaw. I decided that switching the order around would make it easier as the plate doesn't have a bit of rod flapping around making it awkward to weld.

I started with the sliding jaws. For all but one of these, I placed them on the prototype bar (with the half-nut engaged and the jaw frame sitting parallel with the bar) and used a small piece of feeler gauge as a spacer. I've got loads of these little pieces as I bought three super-cheap feeler gauges about 10 years ago and cut them up for use as shim stock when using the four-way tool post that came with my mini-lathe. Now I just use them for odd jobs like this.

The back piece could then be placed on top of the feeler gauge stock, clamped in place and then tack welded. After the first few, I switched from using the cantilever clamp shown in this photo to using a C-clamp as the pliers-style action of the C-clamp is much quicker and easier one-handed.

After putting two tacks at the top and one on the side not covered by the clamp, I took the clamp off, took the frame off the prototype bar and welded up each side.

One of the frames (the one that tilted backwards) had to be dealt with slightly differently. For this one I didn't use the feeler stock and, after lightly clamping the back in place, tapped the back down until the frame sat parallel with the bar. I then tacked and welded as before.

For the screw jaw the approach was very similar. The only differences were:

1. With the sliding jaw, when in motion the back is lifted up and away from the bar. Therefore, the back piece can be safely placed very close to the bar. For the screw jaw, that's not the case so I used a thicker 1.5 mm spacer made up of two pieces of feeler gauge stock.
2. The screw jaw doesn't have the box section all the way through, so I used a spare piece of steel on the front to give the clamp something to bear on.

You can see the clamping arrangement (with the C-clamp, which I used from the start on these jaws) in the photo above.

As with the sliding jaw, after removing the clamp and removing the frame from the prototype bar, I welded the back piece along both edges.

This photo shows all 20 frames ready to have their tops fitted.

 

[Dr.Al]

Fitting the tops was a relatively straightforward process, although I had to skim a little bit of the top of some of the backs with a flap disc in an angle grinder: I think I'd cut the tops slightly longer than originally planned so they overlap with the back rather than butting up against them.

The exact position of the top pieces really isn't that important, so I held them in place with one hand while tacking one corner (without filler rod).

I could then tack the opposite corner and then weld round the three sides.

Rinse and repeat.

 

[Dr.Al]

I'd debated whether to leave the welded outer corners with the weld beads visible or round off the corners, but in the end I decided to give them all a quick go with an 80 grit flap disc in the angle grinder to round everything off nicely.

The jaw pieces could then be fitted to the frames. In the case of the screw jaw frame, the threaded rod has to be inserted before attaching the jaws, but it doesn't need to be welded in place, so for now I've just hand-tightened the other split nut onto the threaded rod to hold it in the hole.

To choose a place for the jaws, there are a few options:

1. Line up the bottom of the jaw piece with the bottom of the cross-piece (in the case of the screw jaw, this is the 3 mm × 25 mm × 50 mm plate and in the case of the sliding jaw this is the bottom edge of the internal box section). This has the disadvantage that the two jaws won't line up with one another, so it's probably best to trim one of the jaws down to match the top of the other. This was my approach for the prototype.
2. Line up the bottom of the jaw piece of the sliding jaw with the bottom of the box section and then line up the bottom of the jaw piece on the screw jaw with the jaw piece of the sliding jaw.
3. As per the previous option, but lower the jaw piece of the sliding jaw until it is at the lowest height that still allows the half-nut to disengage from the threaded rod.

The advantage of the last one is that the bottom of the jaw will be as close as possible to the box section (and parts are likely to be resting on the box section for clamping); the disadvantage is that when sliding it, there won't be two flat surfaces sliding together: it'll be two edges sliding on a flat surface. I don't think that's an issue, so I went with the last option. I did, however, lightly chamfer (with a flap disc in an angle grinder) the rear edges of the jaws to give a slightly smoother running surface.

To work out the position of the jaw pieces, I fitted a jaw piece to a sliding jaw and held it in place with a clamp. I checked whether the jaw could disengage and kept lowering the jaw until it couldn't any more. I then moved it back up until it could just disengage and measured the distance from the bottom of the frame to the bottom of the jaw piece. This worked out as 46 mm. I added a little bit for a safety margin and then cut a spacer to the resulting size: 48 mm. This could then be used as a reference when tacking the jaw pieces in place.

This photo shows the jig I used to tack the jaws in place. It's based on the same fixture plate I used earlier in the project. The two 20–40–80 blocks give a right-angle reference. The two small blocks (one on top of another) are offcuts that happened to be about the right size to offset the body and get the jaw centred. They're held in place with double-sided tape and there needed to be two (actually one cut in half) due to the fact that the body is raised up by the thickness of the jaw. The spacer (marked with its size) sets the offset for the jaw relative to the base of the jaw frame.

This shows one of the jaws sitting on the jig ready to be tacked in place. Hopefully this shows what all the bits are doing. With the body held down onto the jaw with my left hand, I placed a tack in one corner and then placed further tacks in the other three corners (it doesn't need to stay held in the jig for the other three tacks).

This shows what the jaw looks like with the tacks done.

So far, I've tacked all the jaws in place; tomorrow I'll weld round the three sides of the join to complete the frames.

 

[My Old Landy]

I really like the fixturing you have done there. As ever a smart job, looking forward to seeing them complete!

 

[selectedgrub]

Thanks for taking the time to write up, interrupt your work flow to documentate in photos and post for us heathens to drool over.
Too bad alot of people pass over this great thread.

 

[Dr.Al]

Thanks for taking the time to write up, interrupt your work flow to documentate in photos and post for us heathens to drool over.
Too bad alot of people pass over this great thread.

Thanks @selectedgrub

 

[Dr.Al]

Last night I was lying in bed after midnight and feeling completely unable to get to sleep so in the end I got up and did a bit more welding. It really felt like I was getting in a rhythm by the end and I was really pleased with the welds on the last few jaws.

All the jaws have now been welded (except having looked at that photo, it looks like I missed one edge of one jaw somehow (well, it was 1 o'clock in the morning). That won't take long to sort out today.