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Thread: Replacing the CVA compound
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3rd Oct 2018, 10:22 PM #1Most Valued Member
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Replacing the CVA compound
I hope this is on interest to someone. After all the hassle with replacing the spindle bearings, and using the CVA a few times, i have decided the compound slide can go. with the taper turning attachment and the ability to chamfer under power there is no need for it.
I am going to replace it with a solid block and a really too large for the machine qctp ( it wont reduce my swing at all but might make getting up to the tailstock with the LH toolholder hard)
I didnt have any suitably sized cast iron or steel of the right size (5" x 6" x 1.75"), but did have some 5018 aluminium hanging about I hope this doesnt chatter too badly. I dont know what its static rigidity is like but we shall see, worst case ill remake it.
Here are some photos of squaring the block up, I had to use an unorthodox rig to hold it on the long axis with two cheapo grinding vices.
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I then had to do the terrible deed, tap holes in the cross slide, there wasnt a lot of meat in there and due to some features on the underside the pattern wasn't a square but more of a trapezoid, the front two holes are 5/16 and the rear are 1/2 both BSF. No going back now.
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I didnt get any shots of drilling for clearance and counterboring in the top piece but here it all is mocked up
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I then started on the bolt to hold the two together (there is also an anti rotation pin yet to be bored) the only piece of stock I had to hand of the right size was 316 stainless which is pretty horrible to work with so making this took a fair old while. This is the first part i have made on it and i was very happy, super smooth and no lack of power.
IMG_20181002_143812.jpg
I then started boring the through hole for the bolt, im not yet sure how im going the fix the bolt into the bottom bolt, im thinking about milling a slot into the bottom of the block for a 1/2" or so pin that goes through the pin and resists both turning and upward force, worried about the small contact area on soft ali though.
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3rd Oct 2018, 10:48 PM #2Philomath in training
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Chamfering is even easier if you just grind a tool to cut it directly (that is, a tool with a 90 degree included angle). However, keep the compound because you may find it handy in some circumstances. I seem to most often use it when thread cutting. I plunge cut the thread but if I need to adjust the tool position because I've removed the part from the chuck for example I will realign tool to thread by adjusting the compound.
Michael
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3rd Oct 2018, 11:12 PM #3Most Valued Member
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Oh no im absolutely keeping it, and i havent altered anything that would prevent me using it, but i dont think itll be on often unless this really doesn't work out, I do have ground chamfer tools but i find its really handy having both feeds engageable because it saves me a tool holder.
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3rd Oct 2018, 11:55 PM #4.
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Neat setup with the pair of grinding vices Ralph. I was toying with the idea of springing for a modular vice but your demonstration could suggest the purchase of a pair of cheapo vices might be a more versatile and far more economical option.
BT
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4th Oct 2018, 01:08 AM #5
Hi Ralph,
I don't understand why you want an anti rotation pin under the tool holder ?
I can understand why you need a cross pin in the mounting bolt. A round pin through the bolt sat in a groove machined with a ball end cutter would work well.
Whilst my lathe is a lot smaller, there is a grub screw, forming a scotch pin locating and securing the toolpost bolt on mine. Remove the grubscrew and the bolt just pushes out.Best Regards:
Baron J.
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18th Oct 2018, 07:41 AM #6Most Valued Member
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Ralph,
How is this mod working? I'd like to do something similar on my Hercus 260. Do you think it was worthwhile?Chris
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18th Oct 2018, 09:33 AM #7Most Valued Member
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Hi Jack, sorry I haven't had a chance to really use it, I just finished it and then had to go to Japan, as soon as im back I'll let you know. I definitely think I'll have to swap down to a smaller toolpost
I did add one more feature, I put in two blind pockets so the compound retaining bolts could stay where they were avoiding the need to remove the entire cross slide.
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Sorry if they are the wrong way round, can't get to a computer right now to fix them. Have some random Japan photos as an apology.
IMG_20181017_193046.jpg
These little motocompo scooters we designed to fit in the boot of the Honda City.
IMG_20181016_143215.jpg
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18th Oct 2018, 08:47 PM #8Most Valued Member
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Thanks Ralph. Please let us know if you see an improvement in rigidity in your machine when you've had a chance to use it.
Chris
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