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Plinth For Qctp On 9 X 20 Lathe

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savarin

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In my never ceasing search for more rigidity in my lathe I decided to make a plinth for the qctp.
In its normal configuration I can often see the complete top slide assembly flex slightly. (I think I punish my lathe a bit)
After seeing Bill G's plinth I felt it was time to go.
I forgot to take pics as I started but the base was a chunk of mild steel hot rolled plate 19 mm thick.
I faced all sides in the 4 jaw and I must say that facing the sides jutting that far out of the 4 jaw was a bit wild.
The centre hole was drilled and tapped for 14 x 1.25 mm.
The hole in the qctp is 14.7 mm dia so I turned the centre post down to 14.68 mm, it slides on firmly but smoothly.
I needed more height so the central boss is 19mm x 57mm dia. Its bored to 14.68 so the post is pulled down into the hole for a very very tight fit. Then I welded the boss to the base plate.
I made it round so the tool post holders can sit down lower, this allows 1/2" tool bits a bit more height adjustment.
I took a skim from the middle of the base plate to ensure it sat dead flat on the cross slide.
I also took a light skim from the top of the plate to remove all the weld spatter.
plinth-1.jpg


Now I needed a lump of 50mm dia bar and there was none available so I turned a taper into 2 chunks of 19mm plate
plinth-2.jpg

and welded them together
plinth-3.jpg

and then turned and tapped for the 14mm post with a 10x1mm hole for the handle.
plinth-4.jpg

All in place but waiting for balls for the handles.
I hope to try it out tomorow.
plinth-5.jpg

The handle isnt horizontal as it looks in the photo but tilted upwards the same angle as the taper on the top nut.
 
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If it's as rigid as it looks Charles, your problem is solved. I've had mine on there for all od 5 years now.

"Billy G"
 
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brino

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Hey Savarin,

I have occasionally thought of building up a part like that for turning, but one thing always kept me away....I was unsure how machinable it would be afterwards. I always suspected that the high-temp and fairly quick cooling of the weld would mean it was very hard afterward. I have no controllable method of annealing; though I could heat it and drop it in a bucket of ashes overnight.....

Did you anneal it before turning?
Did you find the initial interrupted cut over the weld beads to be difficult?

Thanks!
-brino
 
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savarin

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Hey Savarin,

I have occasionally thought of building up a part like that for turning, but one thing always kept me away....I was unsure how machinable it would be afterwards. I always suspected that the high-temp and fairly quick cooling of the weld would mean it was very hard afterward. I have no controllable method of annealing; though I could heat it and drop it in a buck of ashes overnight.....

Did you anneal it before turning?
Did you find the initial interrupted cut over the weld beads to be difficult?

Thanks!
-brino
Hi Brino,
I dont know any better so just went for it.
No annealing, just used my "metal putting on tool" with general purpose sticks, I let it cool for about 5 mins then dumped it in the sink with the tap on. Steam everywhere.
The initial cut on top of the beads was tough and a bit noisy but once through the surface I barely noticed the difference in the materials.
After the huge interupted cuts facing the base plate sides the welds were small potatoes.:D
Thinking about it now I've never had a problem hacksawing welds, mind you I expect hard facing rods would be another story.
I can just visibly see the difference in the two materials if I look very hard but that maybe just because I know its there.
Those lines that are visible are turning marks that I didnt polish out.
I used hss tool bits as I'm waiting for new belts so cant get up to carbide speeds.
 
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I cut mine from 1 piece, no welding involved. Didn't even use steel. Mine is made from a 1.750X4X4 block of 7075 Aluminu7m. I have no trouble with it what-so-ever. I have even cut threads with it. I do not go along with the 29.5 degree theory. Sure it's a little harder on the cutter but really creates no special problems.

"Billy G"

102_1200 (750 x 498).jpg
 

savarin

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I have even cut threads with it. I do not go along with the 29.5 degree theory. Sure it's a little harder on the cutter but really creates no special problems.

"Billy G"
I'm glad you said that bill, I dont feel such a heretic now.:laughing:
I cut the 2 x 14mm threads on the cold rolled steel post and the 10mm stainless for the handle at 90 degrees with no problems using very sharp hss bit.
 
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That 29.5 degree rule has held a lot of people back from making this mod on the 9x20. I still have the compound but at this point I have no actual need for it.

"Billy G"
 
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While you are doing the cross slide mod there is one more there to do. I swapped out the 8mm lead screw for a beefier 7/16-20 LH. While doing this I made the travel 1.5 inches longer toward the operator.

"Billy G"
 

savarin

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Woa Bill, one at a time:D
I have to make a new nut so I'm considering attempting to cut an acme thread and then make the nut fit that so the extension and real bearing for the screw will be done at that time but first back to the polishing I needed a break from.
 
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when i make my quick release plate 3 years ago i was surprised to find i actually had a 9/16 tap already..lol

IMG_8906.JPG
 
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8mm lead screw to the left with cast nut. 7/16-20 lead screw installed. Does much to add rigidity.

"Billy G"

102_1210 (800 x 531).jpg
 

savarin

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well out of my comfort zone Bill.
Looks very cool though.
Will this be for all the repetitious work required for the radial engine?
Did you cut the 7/16 20 thread or use all thread? (wash my mouth out with soap and water)
 
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Single pointed left hand thread Charles. That's a long way to run a die and hold tolerance and all threads is junk for this. LOL

"Billy G"
 

savarin

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The handle is started
ball-handle1.jpg

then is finished
ball-handle.jpg

with a touch of polish.
So far I have used the plinth for threading and parting.
Parting is an absolute joy now, 40mm aluminium not a problem, 10mm stainless, straight through, no grabbing no juddering just clean cutting with long wavy ribbons.
I'm well happy with it.
 

brino

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savarin,

The handle looks great, but I thought this was supposed to be a break from polishing! :grin big:

-brino
 
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Oily or dirty hands will change your mind about using that polished ball. LOL

"Billy G"
 

savarin

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just for the photo, its already marked:laughing:
 

FOMOGO

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Nice work on the upgrade. Amazing sometimes how effective a small change can be. Cheers, Mike
 

savarin

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Just thought I would post these to show how it now parts.
There is no way I would ever have contemplated doing this with the standard setup.
Just look at those long ribbons of steel.
Just to bring it back to reality, I didnt start the cut with that much overhang.
parting-1.jpg

And the other part that I wanted.
parting-2.jpg

As it came off before I faced it dead smooth.
Now all I have to do is get the blade exactly vertical with some shims and have another go as it did cut slightly curved.
 
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