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Home Model Engine Machinist > The Tools and Tips > Machine Modifications > HF 7x10/12 Lead Screw Mod?

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Old 01-14-2018, 04:07 AM   #21
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My apologies it appears that they don't sell them , i may have been mixed up with another store i buy parts for my mini lathe .
I had a look at some other stores , HF ,Mcmaster carr and shars i can't find one their either .
Try ebay or amazon they may have one on there .
The test bar is just a ground piece of steel bar with a morse taper on one end and a centre in the other .
Not to worry as you can do the same thing with a piece of drill rod ( silver steel ) , precision ground or cromax bar mounted in a four jaw chuck and you want something around 3/4 to an inch in diameter and about6 inches long .
Set it up so 5 inches are sticking out of the chuck then set it so it runs true near the chuck then check the other end hopefully it will be very close to what you have near the chuck - if not give the high spot a tap with a soft hammer usually that is all it will take to tweak it and if you can get the chuck end dead on and the other end within a a thou or two it will be good enough , i usually mark the high spot and indicate along that axis ( high spot mark facing me ) as i know it is high and just subtract it from my readings .
The idea is to mount a dial indicator up on the carriage so it is indicating the side of the test bar facing you then run the carriage back and forth along the bar noting the changes in the readings . Then indicate the top of the bar remembering to rotate the test bar so you are indicating the same side of the bar as you did for the first test ( high spot mark now on top ) . Once again a couple of thou isn't the end of the world .
Another way is the suck it and see test , a 3 inch length of 1 inch dia alloy or brass bar is mounted in the chuck and a length of 2 inches is turned with a sharp tool using a light cut , measure each end of the turned section and compare the measurements , hopefully they are within a thou of each other .
If the vee on the head sits down on the vee on the bed and you can't wobble or rock the head around you probably won't need to worry too much about this test , its only when the head is able to twist or rock because the vee is cut too deep and is not aligning the head to the bed or the head is only sitting on a couple of high spots and can rock around .It sounds complicated but in practise it isn't difficult to do and it can save a lot of head scratching later on trying to work out why the lathe won't turn parallel .

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Old 01-14-2018, 04:43 AM   #22
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I believe have one of those? A live center MT2 came with my mini-lathe. See attachment.

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Old 01-14-2018, 12:47 PM   #23
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Default HF 7x10/12 Lead Screw Mod?

No nothing like it , think more like a dead centre only a foot long .
I think the way for you to proceed is will be fit the head back on and see if it machines parallel .
I will have a dig around on youtube to see if i can find a video of headstock alignment on a mini lathe .
This is the machine it and measure method.

This is using a drill rod test bar method

This is a mt test bar
One end is morse taper the other precision ground parallel and round .
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Old 01-15-2018, 04:11 AM   #24
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Originally Posted by rfresh737 View Post
My tear down for cleaning is now complete.

I'm lucky I live fairly close to the Little Machine Shop here in the Los Angeles area ('close' means within an hour with the kind of traffic we have). In a week or two I'm going to take my spindle case into Chris's shop and install his roller bearings kit. Chris has a hydraulic press to press the bearings which he said he would help me do. I'm not able to do that kind of a job at home.

While I did buy a magnetic dial/base unit for checking my lathe when I start to put it all back together, I am going to stay with my plan and buy his Imperial lead screw/dial kit for the slides while I am there. I can save a little on shipping costs.

I understand I cannot do machining by just using/trusting those dials, so I will get into the habit of cut/measure/cut/measure etc.

I hope we haven't confused you but you can trust the dials to move a slide the amount the graduations imply. The problem is what happens outside of that movement. Deflection will impact how much gets taken off in a cut as can changes in feed rate and SFM. If you are working with materials with a hard shell you can see a difference in material removal when you get into the soft stuff.

The point here that precision work requires measurement. You may even need to allow a part to cool down after heavy machining. All of these dynamic factors impacts your ability to hit size and they are all outside of the movement the slide makes.

Im hoping we haven't left you with the wrong impression in your mind. Having the dials there is a good thing but as a challenge you should tape them off, make them invisible, and machine some parts to size without the dials being visible.

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