[jderou]

Here is a pic of my current situation. Wear in the centers, more so on the right side. After looking at it last night I came up with a game plan. I think I can assume that the very front of the ways and the very back are in good shape. So I can start scraping the right hand side using a flat reference and using a dial indicator set up on the front and back of the left hand way to compare the front and back of the right hand. Then once I get that flat and parallel to the left hand 'corners', I can start on the left side.
What do you think?

[jderou]

I grabbed a couple pieces of ~ 2' pieces of ground bar stock and checked it on a granite surface, and now I know why you can't just use a ground piece of bar stock. So I guess I will be scraping a straight edge. Iron is not an easy (or cheap) thing to come by, is it acceptable to use steel?. I am thinking about taking a piece of 1 x 3 x 24 cold rolled, machining it to fit in the dovetail as was mentioned earlier, then bolting to another piece of stock to make a T-shape, then scraping the top of the T.

[Geof]

If you machine cold rolled bar you will find it distorts into all sorts of wonderful shapes because it has a lot of internal stress from the rolling operation. Hot rolled bar does not distort as much but even this would probably distort far too much for what you plan on doing. To use steel you will be faced with stress relieving or normalizing after a preliminary machining followed by a finish machining or grinding and even then it may be no better than the ground bar stock you checked on a surface plate. Cast iron is used for straight edges and surface plates for the reason that it does not move as much as steel.

[MikeAber]

Hi Joe,

Do yourself a favor, purchase a copy of this book: MACHINE TOOL RECONDITIONING by Edward F. Connelly Copyright 1954.

It explains the procedural steps necessary to accomplish this task, what references are necessary, and how to setup and use the references to monitor your progress.

MikeAber

[jderou]

Out of curiosity last night, I took a sharpened file to the way to see how hard it was going to be. I put my weight into it, pushed, nothing happened! A quick look at my owners manual confirmed it has chromed ways. So now what? It appears that it isn't worn through the chrome anywhere, so in theory the metal underneath should be in good shape. Is their a way to strip chrome?

[mxtras]

.....Is their a way to strip chrome?

With a grinder. There is an electrolisis method also but my guess is that you don't have the equipment to do that and it is my understanding that it is increasingly difficult to find folks that do.

Scott

[nikolatesla20]

Quote from Wikipedia:

The man who scrapes is called a "hand". It is done by using a precision surface such as a surface plate or a straight edge as a standard (a straight edge in this context is not a ruler it is a miniature surface plate of extreme accuracy). A professional scraping tool will be a special made tool, not an old file. The standard is coated with a very thin coating of some material such as Prussian blue. The work piece and standard are touched together by gravity alone and the high spots on the work piece will be colored by the dye on the standard. These high spots are scraped off and the process repeated until there is an even spread of high spots which total about 60% or more of the surface area. If desired the surface can then be “Frosted”. A surface prepared in this way is superior to any machining or grinding operation, although lapping can equal it. Grinding and machining stresses the metal thermally and
mechanically, scraping and lapping do not.

-niko

[Mcgyver]

niki,

the problem with that quote is its out of context - what is being called lapping in this thread is a misnomer, it's NOT lapping as it relates to its commonly understood meaning and what author in your quote is comparing scraping to. Lapping uses a lap against the workpiece. It can be an exceptionally accurate technique. There is however a lap, and the shape of the lap however is controlled. applying compound between two pieces of work is not lapping, as the word/technique is generally understood amongst people skilled in metalworking, or at in minimum it is not a correct lapping technique. so while the wiki is fairly accurate (not a given with wiki's) that quote is out of context to the thread imo.

I've done both flat and cylindrical lapping as well as scraping. One of the themes of this thread I think is that lapping or scraping are not competitors, they are different processes, mostly used in different situations.

[Kipper]

That description Mcgyver gave earlier helped a lot :beer: I often wondered and once I saw that (in my head) it made complete sense. Thankyou bud!

[Cruiser]

Jderou, Cast iron moves around some and is somewhat plastic, if your bed is chrome then i'd suspect more of a settle or sag than wear. even the largest of machines with a huge cast iron body must be leveled and aligned and kept that way as they can and will sag settle and move with warming and cooling and gravity. If it is some settling then you may be able to coax the casting back to where it should be. when i set up my new IH mill, to the table, the first check was the bed for twist and it was close to .018 maybe more, i pulled it into tension the oposite way and let it rest for a few days then in several sessions got it true to within half a line on my sterret machine level, it is staying put for now but subject to change. what would i have had i started scraping or lapping or grinding or ......!

[Nic Scheepers]

Hi there,

This thread has most probably been forgotten already but I tell you one that learned me the most. I have read more or less this whole thread and could not get myself to decide what to do .

My machine(ZAY7045FG) came with very rough gibb strips and one was buckled a bit. This told me I had to do something to improve my machine a bit. Now, learning scraping is going to take a whiile and I cannot get hold of any lapping compound so what to do now.

I decided that lapping with very fine grit sandpaper flat on a piece of glass would do the trick as I woulkd not take off too much, and if I did the gibb strip would be easier to replace than the machine.

I started to take apart the whole machine to prepare for the operation and then started my lapping(sanding) of the gibbstrips. I did not take of too much as I still needed the pockets for the oil. What I did thought when reading the thread was that if I could lapp the strip untill it is very flat, the suggestion of etching some grooves in a diamond pattern was very tempting.

I then washed the whole machine thoroughly and started putting it together again. Now here is where the actual lessons I learned happened. I got to know my whole machine from back to front to the finest detail. I learned I should tram my mill after putting it together, and by the way how to set up my lathe properly, through my wanderings on the net. This was the most learning experience I got. Do not just see this excersize as a mere lapping of the ways or gibbstrips but as a very good learning experience. I now know why they say it is the operator who is good or bad and not the machine you are working with

So do this just for the experience. I did not have any experience in chipping metal before but now a whole new world has opened up.

Now that the blabber is past us I have a question. Nowhere in my wanderings I could find a thread which could tell me how much slack or backlash is permissable in a machine. I know you are going to say "none" but the fact is with a hobby machine there is always a bit of slack. I do have a setting screw that I can set the slack of the feedscew but after tightening it a lot I discovered I still have a bit of slack on the bearings(0.03mm). Looks to me I am going to sit with the 0.03 mm backlash, how much is it on your machine?

Regards

Nic

[mxtras]

This question requires a long answer, but in a nutshell, in any gib arrangement you will have some backlash - you have to unless you want to wear out the ways quickly.

.03MM (.0012") for a precision mill would be a football field, but for a hobbiest it is extremely acceptable in my opinion.

I have more than that in the middles of travel on my second-hand Bridgeport, so I run my machine at the ends instead of setting up in the middle (most of my parts are only a few inches long). I will run for a few weeks at one end, then move the set up to the other end in attempt to wear the machine evenly. I do the same for the saddle - I run near the back, then near the front. I have a central lubricator and I lube the ways almost every cycle. The ways on my BP are worn in the centers but they are chrome, so I chose to deal with it until/unless they get worse. I work around the "sloppy" regions of the machine.

Scott

[SMW Precision]

Hi there,

I do have a setting screw that I can set the slack of the feedscew but after tightening it a lot I discovered I still have a bit of slack on the bearings(0.03mm). Looks to me I am going to sit with the 0.03 mm backlash, how much is it on your machine?

Regards

Nic

Nic,

Yours is at the bottom range of normal in backlash. Most machines will have between 0.002 to 0.006" of backlash. It is not possible to eliminate, with standard lead screws.

[Nic Scheepers]

Thanks MXtras,

I just wanted to get the feel of what is acceptable and what is way out. Your answer tells me precisely what I needed to know.

Thyanks a lot.

Regards

Nic

[Oldmanandhistoy]

Hi all,

I came across this thread quite a while ago now and read some very interesting posts by some obviously experienced scrapers. I added it to my favourite cnczone threads so I could easily find it and use it as reference. To cut a long story short I recently bought a Chinese bench top mill which was in need of some serious scraping. Many years ago now I was given a demonstration by my grandfather who actually did scraping for a living before he retired so I had a good idea of the basic technique. Because I have not read much about the method to scrape a mill I decided to use my initiative and gave a lot of thought as to how I would get the job done. Anyway in another thread I was asked how I would proceed and gave a basic description of how I am doing things. I was kind of hoping some one with the necessary experience might notice and jump in if anything needed correcting. I’m adding the post from that thread here and I hope that some of the posters in this thread will come back and give their opinion on my method. I’ve added some pictures of my effort for your scrutiny also they are from as came, first blue, about half way and the finished part (I was aiming to only remove as much metal as was necessary so as not to need new gib strips for all axes).

DISCLAIMER: I will describe how I did my scraping but I am FAR from being an expert so the methods I used may not be correct. I did think carefully about how I would accomplish the task before I touched anything. It would be nice if someone with experience could read this and correct things if necessary.

In brief how I did my X and Y was to start by bluing up both sides of my saddle using the surface plate as a reference. I then scraped the flattest side of the two sides. Then I placed the saddle back onto the surface plate with the scraped side down. With my DTI I found the lowest point on the four corners, set my DTI to zero and then went back to the other three corners and scraped a reference mark to zero with my DTI. Using my reference marks and the surface plate I scraped the other side. Now I had a reference for my table and the base of the machine.

I did the table next; first checking the table surface for flatness. To do this I used my DTI set to zero on the surface plate with about a 150mm reach. I moved the DTI base to various points on the table and swept an arc watching for any deviations from zero. I am pleased to report that my table was within 0.05mm. I double checked the table with my camel back, from end to end and then across the corners but if you are careful with the DTI this is not absolutely necessary imho. I then placed my table upside down on the surface plate. Again using the DTI I found the lowest point on both ways and set it to zero. Then I scraped reference marks to zero every 100mm on both ways. Using the saddle for bluing the ways and the scraped reference marks I scraped in the table. I again used my camel back a couple of times on the ways to check full length of the table to make sure they were straight but again imho this is not absolutely necessary.

The ways on the base of the machine I did in a similar way to the table again using the saddle to blue the ways and the DTI set to zero on the surface plate to check overall flatness and that both ways were on the same plane to each other.

I hope all that made sense but if not please feel free to ask me to clarify a point if needed.

All this scraping take a considerable amount of time and effort but imho is well worth it; how are you going to make accurate parts on an inaccurate machine. Don’t get me wrong I am not saying that the machine is not accurate enough as it came out of the box but like I said in an earlier post I am a perfectionist by nature so wanted it to be as accurate as I could possibly get it. Also I gave a brief description of how I did it; there is more to it than I described.

One last point; by scraping the ways there is a possibility that the gib’s will no longer be wide enough and may need replacing.

John

While spending the hrs I have so far and with a few more to go I was wondering how much difference all this work would make to my new mill and am I being too fussy taking the surfaces to within +/- 0.005mm (0.0001968498”) (some were +/- 0.03mm (0.001181099”) before I touched them) and the table ways were a milled finish.

If you are interested you can go here http://www.cnczone.com/forums/showth...t=40213&page=4 and see the other posts about scraping that I and another member have exchanged. It would be interesting to know what you folks make of them.

John

[Yrrab]

Have just read the thread on lapping and scraping and am overawed by the knowledge displayed. What I have learned is not to even attempt the exercise but rather to look for a professional. I have an old Graziano 180 with all its bells and whistles still working but would like to improve its accuracy. First steps have been to fit a new chuck and to have the screw on the crossfeed reconditioned (needed polishing and burr taken off the nuts). What is the recommended way to check for wear on the bed? Maybe it may only need adjustment to the gibs and adjusting screws. Any advice will be most welcome!

[Yrrab]

I have read much of the thread describing scraping and lapping. I now conclude that scraping is the physical removal of highspots revealed by bluing using a highly accurate straight edge whereas lapping is the rubbing of the bed ways with a shaped block of something. My questions are: in the case of scraping what implement/substance is used and in lapping is some form of grinding paste used?

[Oldmanandhistoy]

My questions are: in the case of scraping what implement/substance is used and in lapping is some form of grinding paste used?

Hi,
For scraping tools look here. http://www.cnczone.com/forums/showpo...5&postcount=26

For lapping paste here. http://www.newmantools.com/lapping/time.htm#green

John

[Yrrab]

Very greatful to John "oldmanandhistory" for the requested information. Slowly the cloud of mystery around the topic of scraping and lapping is lifting.

However now that I am starting to understand could someone explain the teqniques involved with "V" beds? My old Graziano has seperate bedways for the saddle and tailstock - one side is a "V" and the other is flat. I suspect that the bedways of the tailstock have little wear.

Barry (South Africa)

[IHCNC]

Hi Folks;
Although in the last year and a half we have only sold our mills with ground ways it might be interesting to know how to scrape V bed ways on a lathe.