Is there a better way of holding this piece.

[DPittman]

I need to cut a slot up the middle of this part up to the 1/16" hole. The diagram shows the detail better than my picture. I'm concerned that I can only clamp on the top .100" of the piece with out the saw blade hitting the vice. Is the any chance this can be done successfully this way? Or can anyone suggest a more sane way of holding the piece?

 

[Bradells]

I’m guessing this is your last major operation on the part?

I’d personally put this part on a tooling plate, blocked in with clamps on the base, and held down from the top at the dovetail with some round stock (or a made to fit piece in the dovetail)



Another option (if you were to start over), is to use larger stock, leave the excess behind the dovetail to clamp into the vice, then mill away the excess and then cut the dovetail.

One thing I like and hate about machining is the 'how would I do this ....' usually it's always too late in my case, but each time I learn a little more about how I should have done it .... and hopefully my recall is good when I need to do a similar task next time.


Brad

 

[DPittman]

I’m guessing this is your last major operation on the part?

I’d personally put this part on a tooling plate, blocked in with clamps on the base, and held down from the top at the dovetail with some round stock (or a made to fit piece in the dovetail)

View attachment 10416

Another option (if you were to start over), is to use larger stock, leave the excess behind the dovetail to clamp into the vice, then mill away the excess and then cut the dovetail.

One thing I like and hate about machining is the 'how would I do this ....' usually it's always too late in my case, but each time I learn a little more about how I should have done it .... and hopefully my recall is good when I need to do a similar task next time.


Brad

Good lord man! How did you draw up that schematic so fast?

Yes it is my last machining operation on said part.

I had left extra stock material on the opposite end of the dovetails so I could machine the dovetails easier and that worked well but I hadn't thought about doing the same for the other end. Dohhhh!

Good points and advice, thank you.

 

[Bradells]

Only one gotcha with the above... if those dovetails aren’t the full width of the part, you’ll need a spacer below, else you could ‘tip’ the part.

Brad

 

[Bradells]

Another option would be to place it in the top side of the vice on parallels to raise it up to clear the vice.



I was getting thrown off by your dovetail feature with the first reply ... This would be the 'safer' and easier way to go (as the vice is usually indicated in already)


Brad

 

[PeterT]

The tooling plate setup requires that you have enough room to accommodate 1) the bottom of the slitting saw arbor (the cap) and also 2) the blade diameter is sufficient so the arbor doesn't contact the part. If you have those conditions met, you might be able to clamp part in vise like so. Both setups have their pros & cons rigidity wise but my only concern with tooling plate is top force on the part. As the slotting progresses you don't want the opening slot underneath to see any residual clamping pressure. There are enough things that can go sideways deep slitting in aluminum at the best of times.

Vise clamping tips. A business card type cardboard on the jaws will help makeup any surface unconformities & provide more grip. Parallel under the part will give bottom support. Unfortunately you are clamped on the end of the jaws but sometimes it is what it is. Ideally you would have something like a jack on the other end - maybe your second part?

 

[PeterT]

wow I can barely crayon doctor a picture in the time Brad does a complete drawing LOL.

There are 2 trains of thought on slitting 1) do it in one shot or 2) nibble in smaller DOC passes. If you have iffy rigidity then I feel #2 wins. Keep the teeth clear of chips with a small brush between passes & aluminum likes WD40. Sometimes you just need another holding fixture, sometimes a bigger diameter blade for clearance reasons. I found its important to do a shallow starting cut to guide the blade on subsequent passes & that will give you some sense of how things will go. Maybe 10 or 15 thou. After that the DOC increment is a function of how things are going but slow & steady will probably win the race.

 

[DPittman]

Another option would be to place it in the top side of the vice on parallels to raise it up to clear the vice.

View attachment 10418

I was getting thrown off by your dovetail feature with the first reply ... This would be the 'safer' and easier way to go (as the vice is usually indicated in already)


Brad

Yes I am working on a version of that method right now.

 

[RobinHood]

Another option would be to place it in the top side of the vice on parallels to raise it up to clear the vice.

How I would do it since there is no “holding stock” left on the dove tail side.

Saw/arbor clearance should be achievable; if not, might have to go to a larger diameter saw blade.

 

[PeterT]

I think I misunderstood Brads sketch. Maybe the clamping pin is registered in the dovetail slot? If so, then it wouldn't be applying force over the incoming slit like I was wondering. It is over to one side where the dovetail is unfortunately, so most of the rigidity is served by the toe plates on the bottom. My gut feel is the vise + parallels mode will provide more clamping contact area & clamping force overall. Good luck!

 

[Bradells]

Another option, is to use the vice and a set of parallels to raise the part up high enough to get the saw in..

wow I can barely crayon doctor a picture in the time Brad does a complete drawing LOL.

... my Univ drafting professor hated me (well, my work actually) .... I grew up doing a really rough, barely intelligible 'sketch' with the important numbers, then headed off to the computer to do a 'nice' drawing .... for a decade before heading to school to learn how to draft ...

It would take me weeks to do a hand drawing for class, and it was a complete mess ... line weights 'wrong' (I was using the proper size mechanical pencils), graphite smears, indented/torn vellum ..... my handwriting too 'messy' .. Although now I still get complimented from the cashiers at Lee Valley on my printing on my order forms ....


Brad

 

[Bradells]

I think I misunderstood Brads sketch. Maybe the clamping pin is registered in the dovetail slot? If so, then it wouldn't be applying force over the incoming slit like I was wondering. It is over to one side where the dovetail is unfortunately, so most of the rigidity is served by the toe plates on the bottom. My gut feel is the vise + parallels mode will provide more clamping contact area & clamping force overall. Good luck!

Yup, the pin is in the dovetail .. Easier to draw than a reciprocating dovetail ... Although, per the original drawing, the slot does pass along through the dovetail plane ....

I got sidetracked just looking at the first setup picture, and my brain went "well if they couldn't hold it on the top of the vice, I'd put it on a fixture plate...."

Top of the vice is best!


Brad

 

[DPittman]

so here's how I ended up doing it....maybe a bit unorthodox and crude but it seemed to work ok.

I mounted the piece on a block and used little pins in the existing screw holes to align and help hold things. I also used a drop of loc-tite to help secure. The pictures will better explain what I did.

It's amazing I can cut an accurate slot like that the way my saw blade wobbles about. I only took about .050" cut at a time because I didn't know how much I could do at once and was afraid to risk it.

I only had a frogs hair of clearance left between the saw arbor and the vice at the required depth as can be seen in the one picture.

 

[RobinHood]

Whatever it takes to get the job done without getting hurt... I’d call that a success.

 

[PeterT]

Right on!

The slitting saw is going to give a cleaner surface cut but FYI I have had to resort to my bandsaw on some slits in steel parts. The inside surface of the slit isn't something your eye is drawn to cosmetically. The trick is blade alignment & part feed. So I had to clamp a makeshift fence on my poor excuse for a table. I've had an idea about how to improve this process with 2 identical cheapo mini vises mounted on a sliding plate, but the need hasn't risen enough to warrant the expense yet.

I've had to use CA glue or epoxy as temporary holding adhesive for finicky parts. They don't like shock or vibration like interrupted cuts. The part also needs to be tolerant of heat to soften the adhesive to release it from the fixture. Its best to have a secondary mechanical clamp in conjunction like what you have done. Epoxy is thicker viscosity so its a bit more forgiving of surface gap & you can build up reinforcement fillets. Once heated it just softens & part comes off quite reliably. Aggressive double stick film has promise too but I haven't found a reliable way to release it. Heat turns it into a gooey mess. Same with solvents & I have an arsenal at my disposal.

 

[PeterT]

Not sure how much clamping pressure is required to hold the part on, but you did the right thing with a stress relief hole. The lower down the bolt is & larger the relief hole is, the better it will clamp for the same amount of bolt torque. You also don't want to strip the threads tightening, so larger hole would be the next step if you find yourself gronking. Just terminating the slot square from the slit like the drawing shows might work fine too, but part may be prone to a crack developing one day although aluminum is pretty ductile.

 

[DPittman]

Not sure how much clamping pressure is required to hold the part on, but you did the right thing with a stress relief hole. The lower down the bolt is & larger the relief hole is, the better it will clamp for the same amount of bolt torque. You also don't want to strip the threads tightening, so larger hole would be the next step if you find yourself gronking. Just terminating the slot square from the slit like the drawing shows might work fine too, but part may be prone to a crack developing one day although aluminum is pretty ductile.

Yes this scope mount design is an extremely delicate thing and I wish it allowed for a bit more rigidity and clamping force. Those screws are only 3mmx0.5. There isn't much material on the thing to make many modifications (like lower screw or larger hole) but I wanted to follow the original plans as close as I could anyhow.

 

[Tom O]

I have used the masking tape crazy glue with good success another way is with cerro bismuth low melting point metal I have some if your in Calgary.