Thread: Cross slide scraping

Originally Posted by simonl

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.

I have a handle on my Buniax(power scraper), just let me at it I'm not sure I'm very good with it........ but I am sure I'm a lot better than I was with it.

Phil didn't cover part yet

I was thinking about checking the cross slide back on the carriage in the morning , but I'm not sure there is any point to that. They will both need to be flat one day. Though maybe the cross slide has been scraped to a banana carriage?

Stuart

Originally Posted by simonl

Hi Dave,

When you say warped. How warped do they get from stress relieving? Are you talking millimetres over the length of a table or is it 1/100's?

Cheers,

Simon

The last one I had was 0.2 down at the front one side, and 0.3mm up on the other side adding up to 0.5mm warp over all. They tested another one and found it the same, and then told me it was no good to me either, not good to anyone other than using it as a drill press.

When I told the service department guy about the warped table, he said what are you doing machining out there anyway, just got to laugh at the lack of knowledge, and these guys are testing and inspecting the machines.

I measured every corner of the table for thickness and it was spot on all the same, so the problem was a warp. In the end one worker did admit it, and they already had a container of new mills coming until the other manufacturer got there act together, there words not mine.

The new one I got had a hardened table so that took care of that, but when Ray bought his it was not the same as mine, so I think the problem was sorted and they went back.

The first one I had was ground wrong and had a taper of 1mm over the 1 meter table length, but no warp.

Dave

You are right - bending it in a press would be tricky (I was in a rush last night and thought "lump of silvery metal = steel").
Can you clamp it to a strong back with a counter bend in it (to allow for spring back) and then stress relieve? That might lessen the problem.
The more straight forward option is to machine say 2 to 4 thou off the surfaces, but if the dovetail is banana'd (likely because the rest is too) you would need to machine it out. As soon as you do that you've widened the dovetail. (3 thou depth on a 60 degree dove tail = around 2 thou sideways; both sides is around 4 thou?), which may mean a new gib if the old one is near the end of it's adjustment - even more possible if the old one is banana'd too.
Scraping down to flat would be a lot of work and the inside stuff would be difficult.
Checking the mating part is a good idea. If that's not flat you may be better off scraping one to the other and living with the knowledge that your tool heights will vary slightly depending on the diameter of the part being turned.
Michael

The top is kind of irrelevant compared with the sliding ways.

I'd scrape the bottom flat not worrying overmuch about the top at this time. Deal with the dovetails as best you can but you really need the bottom flat as it'll rock on the ways as it is which will encourage dig-ins when parting off at least.

To deal with the top, once the bottom is flat, just put the thing on a surface grinder or mill and take a skim cut over it. I might reduce the non-bearing area by a few thousands and then scrape in the surface that the compound swivels on or I might not. Main thing is, get it flat and parallel with the bottom.

Better check the cross slide ways while you're at it....

My big Monarch has some similar issues but that's 70 years of use. I'll look at it once I get the surface plate home and have some spare time.

PDW

Does machining create stress? In cast iron I mean. Pretty sure bending would. I would avoid both and just scrape it. You have the mighty Stuax, go to it.

With my compound I just made a straight edge from a hunk of MS bar with a 45 deg angle. Scraped of course. Worked fine. You will need to pay attention to clearance grooves. But you knew that. I would be more worried about screw/nut alignment than the gib. Gibs can easily be shimmed or replaced. I say easily but I must admit the gib was the trickiest part for me. I rescraped the old one and shimmed it. If I'd made a new one I might still be there.

Originally Posted by simonl

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

Cheers,

Simon

Yes. There will be a gallery of interested onlookers.

Originally Posted by PDW

The top is kind of irrelevant compared with the sliding ways.

I'd scrape the bottom flat not worrying overmuch about the top at this time. Deal with the dovetails as best you can but you really need the bottom flat as it'll rock on the ways as it is which will encourage dig-ins when parting off at least.

To deal with the top, once the bottom is flat, just put the thing on a surface grinder or mill and take a skim cut over it. I might reduce the non-bearing area by a few thousands and then scrape in the surface that the compound swivels on or I might not. Main thing is, get it flat and parallel with the bottom.

Better check the cross slide ways while you're at it....

My big Monarch has some similar issues but that's 70 years of use. I'll look at it once I get the surface plate home and have some spare time.

PDW

I'll swap you your 70 year old Monarch for my BRAND NEW Chinese 12x36 anytime!

Hurry though, this offer won't last!

I'm still not sure about cast. I dont think you can machine stress into cast. You could remove stress with machining or stress the part by clamping, machine it and have it move back when you unclamp it.(at least at our levels of accuracy)

Hi BT,
I'm still thinking back to your struggle getting your block parallel...... just how far out was it again?

I think scraping the bottom will be easy, just because there is so much less than the top.

Stuart

p.s. I should add I think I will skip the advice in MTR page 260 about using test bars in the crossfeed nut. If I scrape the bottem flat to the corners I think that will be damn close to straight down(I'l check again). Then one the top is scraped parallel to the bottom if the feed nut is giving issues(which it shouldnt) I can machine there the nut sits............. I think

Originally Posted by Stustoys

I'm still not sure about cast. I dont think you can machine stress into cast. You could remove stress with machining or stress the part by clamping, machine it and have it move back when you unclamp it.(at least at our levels of accuracy)

Hi BT,
I'm still thinking back to your struggle getting your block parallel...... just how far out was it again?

I think scraping the bottom will be easy, just because there is so much less than the top.

Stuart

Three and a half thou Stu. Sounds like FA but as my benchmates at the Fest can attest, I definitely made a meal of it. The 0.015" on my grinder ways will make the block seem like a tidbit in comparison.

In regards to machining stress into cast iron, I will either transcribe or photograph a couple of paragraphs from Wayne Moore's Foundations of Mechanical Accuracy, addressing that issue. There is also a paragraph or two dealing with casting seasoning that may be of interest.

BT

I don't know is you have already checked your cross feed nut, but mine was high and needed to come down with a few shims.

Dave

Originally Posted by simonl

I'll swap you your 70 year old Monarch for my BRAND NEW Chinese 12x36 anytime!

Hurry though, this offer won't last!

Thanks all the same, I think I'll keep the beast. Somehow I think I'd have trouble cutting a 2 TPI LH square thread on a 2" dia shaft on your lathe.

PDW

Originally Posted by PDW

Thanks all the same, I think I'll keep the beast. Somehow I think I'd have trouble cutting a 2 TPI LH square thread on a 2" dia shaft on your lathe.

PDW

I wasn't expecting success with that offer! The first time I saw a pic of a Monarch was when a member posted a pic of theirs (it may have been you, not sure but it was dark red) and I thought what a lovely lathe. It then prompted me to do a search and I died when I saw what they sell for! I can only assume you do get what you pay for!

Oops sorry, back on topic.

Cheers,

Simon

Whatever you do my only advice is.....

PLAN PLAN PLAN...

Originally Posted by Dave J

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

I use IDM (Internet Download Manager) which I paid for but a freeware version was available. I have used it for years. It downloads stuff much faster than IE or Firefox. When I click on a You Tube (FLV) video a button appears at the top of the video as it is loading asking if I want IDM to download it. I then close the video window and wait for the download to finish. Very customisable. Can also alt click on a file name ie PDF and select download with IDM. Can also download every file on a web page. A window appears which allows you to select which ones to ignore and download the rest.

I then watch these videos with VLC Media player which is freeware with a GNU public licence. I can vouch for both of these programs.

Dean