Small hold down clamps for my HV-6 rotary table

[WobblyHand]

Here’s how I’m attempting to make the large dove tail for my steady rest . I might try the same with the clamps . Had to make two tools , the one i did for the angle worked ok but kept burning going across the flat though maybe the SFM got too great because I had to extend it , it was hitting the top edge . I slowed it down and rounded the bit I used for the flat seems to be working better but had to quit to help the wife

That's a pretty big dovetail. Extending the length of the fly cutter, will increase the SFM.

I have a 3/4" HSS dovetail tool. Originally bought it to make an OXA boring bar holder. (Made the toolholder out of 7075.) I'll use the dovetail cutter tomorrow on my prototype aluminum clamp. Once I work out the final length of the clamp, I'll adjust the drawing and make the real ones out of steel. My dry run should help speed up the machining of the actual clamps.

 

[WobblyHand]

First attempt failed. Seems like the teeth are too close and not deep enough. Guess that's why one makes a prototype!

Maybe I didn't measure well enough. It seems I got a last 7th step, indicating my spacing is off. There should only be 6 steps. Either my measurements, math or my quill DRO is off. (That narrows it down ) I calculate the z drop per step is 0.07232" per step. My quill DRO only measures to 0.0005", so I set the drop to 0.0725".

Interesting problem... Have to think about this one.

Edit: Looks like mensuration error at the beginning. Wow, how could I be off by a factor of almost two on the step height?
Literally, back to the drawing board!

Well, at least there are less teeth to cut!

 

[WobblyHand]

@Alcap don't use my dimensions. The ones I posted are wrong. I'm coming up with some better values. When I cut them and see they are good, I will update the drawings. For a 10mm clamp there should only be about 4 teeth, with a vestigial 5th. Not only was my clamp model wrong, but so was the model I made of a step block. It appears the spacing between the teeth tips is 0.125" if measured along the 60 degree slope, and stays that way for the 12 teeth in a row that I measured. I may look at that under a microscope, to be sure.

The hard part for me is doing the (correct) constraining of the drawing. The teeth tips have to follow a 60 degree slope. I'll give this another go tomorrow. Weather will be poorer tomorrow and I won't feel too bad about being below ground in my shop.

 

[WobblyHand]

I have a drawing that should be ok now. Still, I am holding off posting it tonight. When I cut the teeth tomorrow, and they are reasonable looking, I'll post a picture and the drawing. Spent a lot more of my day wrestling with FreeCAD, and forcing constraints, than I planned to! Learned about taking reference measurements to check my work. So I learned something out of this

 

[WobblyHand]

Cut some teeth this morning. Came out ok. Not machinist perfect, but not bad

Good enough to continue machining. Machined to length and put in the slot. To lazy to change the end mill and got some striations in the slot, but I expected that. Guess I will try to do it better for the steel clamps. The slot length is to print, but in my opinion, there's no need for the slot end to be 1mm from the tooth. I will reduce the length of the slot from 24 to 22 mm.

So after cleaning up the piece, I took it to the fixture plate to check it out. It seems to be functional but it's clear I will also need other clamp styles to get full use of the small fixture plate.

Can't complain about how it's coming along. I'll try to finish this today, accumulate some changes, make drawing updates, and post results. Although this is a small piece, it sure has some interesting things that you have think about.

 

[WobblyHand]

So I made this. It has its flaws, but it is fine. The prototype has served its purpose.

Thought I would start on preparing the steel stock.

Somewhat foolishly, I thought I could use a slitting saw to slice some 5/8" x 1" steel stock into two 5/8" x 1/2" pieces. The stock was about 4-5/8" long. I chose a 2-3/4" OD slitting saw with a 1" arbor. Yes, the cut was 5/8" deep, but I checked to make sure I wouldn't hit the arbor. Two things went wrong. One was the mill just doesn't have adequate speed control at the required low speed. This is partially because there is insufficient RPM feedback at 140 RPM, and part due to the fact that the motor itself has insufficient torque. So the motor would bog down, speed up, over speed, etc. Not much fun, but survivable.

The other thing that went wrong is the thin blade mistracked and decided to cut downwards. I didn't notice this, as I was screwing around trying to keep the motor in its sweet zone. Well the cut (and the blade) kept slowly going downward, until there was a crack. Shutting everything down, pulled the slitting saw out of the cut. Turned the motor on and saw the blade was wobbling, and lower than the entry point of the slit. Turned it all off and removed the arbor from the mill. Unscrewing the arbor, the blade sort of fell off. I thought, this is strange. Umm, something is wrong with this saw blade.

It is pretty thin at 0.020", but I really hadn't anticipated this failure. I have other saw blades, but I need to do something about making slitting more tolerable. It's too darn slow, and takes too much human interaction. Feels like it is time to make some pulleys for the mill, to get the motor speed higher where it has more torque and the spindle speed lower.

 

[WobblyHand]

Nothing much to show, but I discovered a few things:

1) The SA-1000 arbor was defective out of the box. The arbor screw was drilled off axis and had 0.036" runout. The head of the arbor screw interfered with the arbor cap causing the arbor cap to tilt under some rotation angles. The tilted blade wandered off until it was restrained by the arbor and then the blade fractured around the outer diameter of the arbor. I contacted my supplier today, that the arbor was defective and they agreed to replace it. I should have a new 1" saw arbor tomorrow.

2) I had set the pulleys incorrectly, staying in high speed mode. Therefore the mill had practically zero torque in the 100 RPM region. Today I discovered this and put the pulleys in low speed mode and was able to cut the steel stock using a 2" diameter, 1/16" thick blade, using a 1/2" arbor.

3) The speed control regulation at lower RPMs on my mill is poor. There are dead spots in the speed setting potentiometer. I could not set the speed I wanted, I could set higher or lower, but there was over a 50 RPM hole.

 

[Parlo]

You could also use an internal threading bar with a 60 degree insert in a collet to machine the grooves.

 

[WobblyHand]

I dug out my 1/2" arbor, and found a cheap Grizzly 2" diameter 1/16" thick saw blade. Mounted it up on the arbor, set the pulleys in the all important low range position and was able to slice through the 5/8" thick 1018 steel stock. Was happy to have gotten that slitting problem under my belt. McMaster shipped a replacement 1" arbor to me, should have it by this evening.

Today, finished up bringing the pieces to size. Milled them to 10mm x 14mm. Then used the same 2" saw to cut them to 52mm length. So now have 4 blanks ready to machine into hold downs. So not exciting, but some forward progress at least.