Thread: Adustable Parallel !

Hi Guys,

I've finished milling the slots ! Both half's of the parallel now have the 3 mm wide slot cut into them.

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In order to mill the slot in the other half, I just swapped the places of them. Since the rear vise jaw was used as the reference to centre the slot. That white bit is a cardboard packing, because the wood and the two workpieces are the same thickness.

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These are the two workpieces ready for slitting one of them. The little slitting saw blade that I propose to use is the one in the picture. Whether it works or not we shall see, though I won't be running it at anything near the speed marked on the blade.

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The two parts as the will be when assembled.

I need to drill and thread a hole for the clamp screw before I figure out how to mount one of the pieces for slitting it. I also want to add the details to the drawing.

Thanks Guys.

Hi BaronJ
On my set of parallel's most of them have two clamping screws and they are made with dovetails. As your design is of the slot style I think you would need two screws on all sizes. Your brass strip should slide nice. My set are Chinese and as usual I had to do quite a bit of de burring and grit removal to get them to work, good now.
Bob

Hi Bob,

I'm only going to use a single screw on this one ! I've no plans for making any more of them. If I'm honest it was more an intellectual exercise to see if I could make one. I've yet to figure out how to secure one half for slitting. The hole drilling and tapping isn't going to be a problem, neither is making a large head screw.

That slitting saw is the thinnest that I have. Although its intended to be used with a Dremal style tool, it should work allright to cut the workpiece.

What's your concern with securing for slitting?

I was thinking you'd just lay it horizontal on a packer and clamp it down in a couple of places (outside the slit zone).
Start from one end then once you've got in sufficiently insert a packer/shim inside the slot so you can clamp the cut end. Continue to pack and move clamps as you progress.

Steve

Hi Steve, Guys,

Thankyou Steve, yes I see what you mean ! My initial thoughts were I'm not going to have enough room under the saw blade mandrel to clear the mill vise top. At best there will only be 4 mm material thickness. If I can clamp it in a way that I can get it square and rigid enough. A horizontal spindle would be ideal for this.

I wonder if I could get away with using the lathe ??? I'm going to have to think about it for a while. The mill would be first choice, because of the ability to control the speed, where as the lathe would be fixed at what ever I set the belts at.

Changing the subject slightly, I've done the drawings to take into account the work done and the changes made.

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I hope that it is readable, png pictures are not the best for showing detail.

John, Thanks for the how to and the drawing that I can read without my glasses.
A very intresting project.
Kryn

You don't get any advantage (mechanically) by making the bottom of the slot parallel with the bottom of the 'parallel', so why not make it an even depth from the angled surface. That then gives you some room to clamp on that un slotted material...

Michael

Hi Michael,

Thankyou for your reply !

Originally Posted by Michael G

You don't get any advantage (mechanically) by making the bottom of the slot parallel with the bottom of the 'parallel', so why not make it an even depth from the angled surface. That then gives you some room to clamp on that un slotted material...

Michael

Sorry but you have me a little confused here ! The slot at the top is 3 mm wide and 1,5 mm deep. The 0.8 mm wide slit going to within 3 mm of the bottom is intended to allow the sides to be compressed by the screw so the the slot can close up on the piece of brass fastened in the top piece, locking the two parts together.

At this moment I'm not even sure that slitting down to within 3 mm of the bottom will allow the sides to flex sufficiently to clamp the brass strip.

Originally Posted by BaronJ

Sorry but you have me a little confused here !

Simply that if the slot at the narrow end is say 8mm deep, having a slot at the 'tall' end say 18mm deep won't give you any benefits; it may make the clamping a little lop sided. You still have to get the 8mm deep slot ot narrow to clamp the brass strip though, even if the 18mm end takes less force to close.

Originally Posted by BaronJ

At this moment I'm not even sure that slitting down to within 3 mm of the bottom will allow the sides to flex sufficiently to clamp the brass strip.

There's one way to find out...
You could try a variation of a cotter clamp but with a square notch to clamp the strip, relying on the round cotter in the hole to retain things a good fit would be required though)

Michael

Hi Guys,

Having thought about how I was going to saw the narrow slit in one of the half’s of the workpiece, I've concluded that the lathe is the way to go. So my thoughts are clamp the workpiece on the lathe cross slide and turn the saw blade on a mandrel using the chuck and using a live centre in the tailstock to support the other end.

Which leads me to a question ! Do I cut the slit first, or do I drill and tap first ?
I've still to make a flat head shoulder screw, so I might do that next.

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I dug a six inch long piece of 1/2" bright steel rod out of the bits bin and cut it in half.

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I then drilled and threaded one half to take an M6 thread. The other half was turned down to fit the 1/4" inch (3.35 mm) hole in the saw blade. I then turned the end 3/8" inches length down to 5.85 and threaded it M6. I used a die to cut the threads and had to turn the die around to get the threads right up the the 0.6 mm shoulder. Even then I had to countersink the female threaded end in order for it to close up right up to the head.

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This is the finished mandrel. It traps the saw blade nicely, though I admit that I used the lathe chuck on one end and the tailstock chuck on the other to tighten it firmly. I'm thinking that I might be wise to put Tommy bar holes in either side.

I'll post pictures of the complete set up later. I just need to find the vise that fits on the cross slide !

Thanks Guys.

Hi John,
Looking at your latest drawing, I think you have planed on using a single 6mm screw for clamping. On my set the clamping screws are only 3mm, by using this smaller size you will get a lot more threads.In use I often use my parallels as outrigger supports for longer jobs, having two locking screws ensures that the parallels do not slip when used like this and two screws also allows you better access to lock the parallel. I would make the slitting saw cut an even depth from the bottom of your 3mm slot to ensure even clamping.
Bob

Rather than drill tommy bar holes, would it be easier to put a couple of spanner flats on it??
Kryn

Hi Bob, Kryn, Guys,

I did decide to drill the screw hole first on the basis that once I slit the workpiece I would not have any support between the sides without using a filler of some kind. I did use M6 for the threads, I wasn't sure that fine threads would have been strong enough ! Bob, thinking about what you have said, I should have used a much smaller screw. Then if I stripped the threads I could drill it out re-thread it and use a larger screw.

Kryn, yes spanner flats would be better than Tommy bars ! So that is what I'll do. The only thing that I have to take care about, is if the blade gets too hot and dishes in use.

Thankyou both for your suggestions

PS. I still haven't found the topslide vise.

Hi Guys,

I still haven't been able to locate where the lathe topslide vise has been hidden, so after spending a couple of tiring hours shifting and looking through boxes and trays for it, I've given up on it. Its around somewhere.

So I decided to make a one off jig just to cut the slit using the 0.8 mm thick saw blade.

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I removed the front and rear tool posts from the cross slide and placed the plastic protector into the mounting hole to protect table drive gears underneath from any swarf.

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Then using one half of the workpiece decided where about to place the jig.

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I used a block of pine and cut its thickness so that it cleared the saw blade giving me the amount of depth that I wanted to leave 3 mm at the bottom. Actually it ended up just a fraction less. I also marked where the "T" slots would be when placed in the right position for the slitting.

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I then drilled 8 mm diameter holes for the original Myford "T" bolts that I used to clamp the wood down to the lathe cross slide. I fastened two pieces of metal to form side and end stops for the workpiece. Since the direction of cutting would try to push the workpiece away and under the saw blade jamming it and possibly breaking the blade.

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This shows the jig fastened to the cross slide ready for slitting. I used a bit of scrap and the two off cuts from cutting the workpieces, forced together forming a wedge between the nuts and scrap to hold the parallel in place. The parallel only just cleared the mandrel holding the saw. I ran the lathe on its slowest speed without using back gear and Trefolex as cutting oil.

Part two later ! I've been called for dinner...

Hi Guys,

Sorry to rush off for dinner, family meet up ! More than my life was worth to be late !

Anyway to continue.

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With the jig in place and all setup ready to go. A slow steady feed resulted in achieving a smooth bottomed slit down the length of the workpiece. Note that this is effectively climb milling so the cross slide is constantly being pulled towards the saw blade in the direction of the cut. This means that you have to go quite slowly to prevent the blade digging in. By the time you have got halfway down the length of the workpiece the blade is no longer trying to pull the work into the blade, and it becomes much easier to control. By the time that you have got to about 15 mm from the end of the cut, you are now pushing the workpiece into the blade. The transition from the blade pulling the workpiece to having to push the workpiece is very subtle, and at one point seems as if the blade has stopped cutting, which it hasn’t.

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As I mentioned earlier, I have drilled and threaded one half of the workpiece M6. There is only need to drill clearance for the shoulder of the screw and the counter bore for the screw head to be done. I've yet to make the screw ! I am going to turn it from a piece of 10 mm diameter silver steel rod and use the saw to cut a screwdriver slot across the head.

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These pictures show the before and after milling the slot and cutting the slit in one half.

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This is the finished slit. I placed the two pieces side by side as a comparison.

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Note that the slit didn't quite make it to the bottom of the slot at the narrow end.

I have cleaned up the burrs raised with a scraper, so the bottom of the slot is sharp and square on both pieces.

Thanks Guys for all the advice and useful comments. I hope to show the finished product soon.