Thread: Cross slide scraping

Stuart, I'm wondering whether you would be better off using a press to try and get things straighter. My concern is just that you can scrape the bottom flat but the inside of the dovetail will still be banana shaped. That will be tricky to scrape (if only because of access). I can't picture what the form will look like, but the less you have to remove the better off I think you will be.

Michael

Hi Micheal,
I'm not exactly sure how much you can bend(as apposed to flex) cast iron?
The crash may have nothing to do with the banana.
Maybe I shoud do some reading on normalising cast iron?

Stuart

p.s. Maybe I meant stress relieving?

Originally Posted by Stustoys

Hi Micheal,
I'm not exactly sure how much you can bend(as apposed to flex) cast iron?
The crash may have nothing to do with the banana.
Maybe I shoud do some reading on normalising cast iron?

Stuart

Not knowing much about this topic yet, i don't know whether i'm just talking out my ####, but have you actually checked the dovetails for straightness? Personally i wouldn't put cast iron in a press, the risk is pretty high, especially if it has already been bent, depending on the cast as to whether it can be normalised, and if you do it will probably need re-machining anyway.....

Nick from Germany ( I think it is ), has you tube videos of scraping the cross slide of a Chinese lathe like ours along with showing you how to scrape the gib in.

Dave

I suspect the chance of having bent it is pretty slim.
I suspect more thatis was never straight or has had some internall stresses which have 'relieved' themselves....
To ensure that you toolholder remains truely vertical, you might have to scrape it parallel to the centre section of the toolpost circle - on both top and bottom.... and the dovetail. Sound like a lot of work if it actually is 2 thou out end to end.....
On the other hand, I might well be off on a tangent that is purely ficticious
Joe

Originally Posted by Ueee

Not knowing much about this topic yet, i don't know whether i'm just talking out my ####, but have you actually checked the dovetails for straightness? Personally i wouldn't put cast iron in a press, the risk is pretty high, especially if it has already been bent, depending on the cast as to whether it can be normalised, and if you do it will probably need re-machining anyway.....

It's an interesting situation. I would have thought that if booth sides, top and bottom show deformation then the dovetails would have to be the same. I guess running a DTI across the dovetails while on the granite would show a better picture.

The use of a hydraulic press to reduce that amount of scraping would surely be a very delicate process. However, leaving it the way it is and scraping the top and bottom straight down will still leave the dovetails with the curve.

Good luck with your decision, I will watch this thread with interest.

Cheers,

Simon

Originally Posted by Dave J

Nick from Germany ( I think it is ), has you tube videos of scraping the cross slide of a Chinese lathe like ours along with showing you how to scrape the gib in.

Dave

Yes, I've seen some of his videos. His name is Nick Mueller.

Simon

hi Stuart. i have a feeling this will be a great thread.
can you please work on it endlessly so we all know how it goes in the near future.
my first question is how are you going to check the top part for flatness and parallel to the bottom part?
and ueee mentioned checking the dove tails for straightness. how would you do this?
I love it when some starts a thread on something ive been thinking about.
aaron

Originally Posted by simonl

It's an interesting situation. I would have thought that if booth sides, top and bottom show deformation then the dovetails would have to be the same.

Stuart,
You didn't actually say whether the top surface is bowed too.....just imagine without things made poorly in China, you would have nothing to do!

Ewan

Nicks video's where posted here a while back, I am sure RC will know where to look for them and hopefully post them here.

I did get a program to down load videos from you tube but it never seemed to work, if Nick ever takes them down all will be lost, as he did some really good ones that would benefit a lot of guys learning this art.

Dave

Hi Guys,
Having trouble keeping up with all your comments
All answer a few of the easier ones.

Originally Posted by Ueee

You didn't actually say whether the top surface is bowed too

I sort of did but I guess I didn't explain the pictures very well
In the first picture the top of the cross slide has been spotted(its only touching on the ends.
In the second picture the bottom has been spotted and its only touching in the middle. Also there is a 0.002" feeler gauge in the middle of the "bow" of the top side.
In the third picture there is a 0.002" feeler gauge under the end. I should have used two feeler gauges but its loose on 0.002" so I'm pretty sure I'm not rocking it.

Originally Posted by azzrock

can you please work on it endlessly so we all know how it goes in the near future.
my first question is how are you going to check the top part for flatness and parallel to the bottom part?
and ueee mentioned checking the dove tails for straightness. how would you do this?

No promises on that I reserve the right to put the lathe back together at any time.
You pick one face, make that flat. Then make the other face flat while making it parallel at the same time by measuring the corners and making them all the same height.
I will have to buy/make a straight edge to do much work on the dovetails I'm thinking that over ATM.

Originally Posted by Dave J

Nick from Germany ( I think it is ), has you tube videos of scraping the cross slide of a Chinese lathe like ours along with showing you how to scrape the gib in.

Yes I've seen them, he makes it look to easy

Originally Posted by Ueee

but have you actually checked the dovetails for straightness?

no but I have a couple of ideas. But I think the done thing is to get it flat and parallel first then worry about the dovetails.......(?)

Originally Posted by jhovel

I suspect the chance of having bent it is pretty slim.
I suspect more thatis was never straight or has had some internall stresses which have 'relieved' themselves....
To ensure that you toolholder remains truely vertical, you might have to scrape it parallel to the centre section of the toolpost circle - on both top and bottom.... and the dovetail. Sound like a lot of work if it actually is 2 thou out end to end.....

The more I think about it the more I agree with you Joe, how could it have been bent while it was still on the carriage dove tail?

Scraping top and bottom parallel should give me a vertical tool post.

Did I miss anyone?

Stuart

Originally Posted by simonl

Yes, I've seen some of his videos. His name is Nick Mueller.

Simon

I never refreshed this page before posting and then all of a sudden here are all these replies, LOL

Nick used to post on Home Machinist a few years back and when he made the videos he gave us a link, and I think with everyone asking him questions it prompted him to do more. Then some crap hit the fan with some members and he left and has never come back, sad as he was a talented guy willing to share his knowledge.

Dave

With the bending it's probably like the episode of the HM52 mills with the warped tables. They never aged the castings so on the way over and while they sat in the shops the warped as they stress relieved themselves.

You hear of the old manufactures throwing castings out in the weather for 6 + months to age a bit before machining, I would say the only aging the Chinese casting get is the ride from being poured to the machinist/assemblers, and thats only if they are different companies as some do everything in one shed.

I also agree yours has probably slowly stress relieved over time as you have had it a while now.

Dave

Scraping top and bottom flat and parallel should be a walk in the park for you!

Scraping the dovetails flat and parallel (to the bed and eachother) will be the fun bit. I look forward to that part.

I hope this thread runs a long course. I think there may be a few of us that have these style Chinese lathes and have a similar cunning plan in the pipeline to improve them.

Cheers,

Simon