Hand scraping for a beginner

After watching a few videos on 'hand scraping machine ways', I am tempted to do some myself for the dinged and dented ways of my aquired ML7. Can someone answer some general questions:

1. Have grinding machines have made hand scraping way redundant? If not, then wha are the unique advantages to hand scraping (aside from expense)?

2. Are a surface plate, marking paste, and scraper only required tools?

3. Is it something that truly rquires lots of skill, or more accurately: pateince and attention to detail.....This point is best explained by my experience in another hobby (7mm scale railways); I was led to believe that as a newcomer it would take *many* models before achieving a 'cabinet stand' finish. However after thorough research and a couple of practice models, I have achieved excellent results. I therefore struggle to see why some modellers are so daunted by painting.

Any advice gratefully received.

Edited By choochoo_baloo on 18/07/2017 21:05:20

A small lathe like a Myford can have the bed reground - it might cost a bit but at least it should be accurate. As well as the bed, there is also the headstock, saddle and tailstock to consider. A ground finish is not as good as a scraped finish as far as oil retention goes (or so we are all told, but all the lathes on the market seem to think it is fine).

If you really want to do some scraping you'll need more than the tools you listed - a long camel-back straight edge would be useful, as well as a couple of 0.0001" or 0.001mm test indicators plus mag base stands for them. At least half the battle is knowing what to measure, and from where (in other words, where you place the mag base, so you take a meaningful measurement). There is a book on rebuilding machine tools that would seem like a good start.

Like any hand tool technique, you would probably want to practice on something smaller to start with, like an angle plate. As good as YouTube is, there is no substitute for practice. That is where I would start - have a look at some of the small projects that YouTube contributor Stefan Gotteswinter has done - he clearly knows what he is talking about and his videos are a good example of the sort of measuring and indicating that has to be done at the start of a scraping project.

Speak for yourself, I have wholeheartedly embraced weathering as an alternative to skill in painting

Neil

More seriously, scraping is not a way to get rid of dings and dents, although it is a useful approach for getting rid of any high spots thrown up by them. It is finishing operation and very little material is removed.

Unless the bed is worn, treat the odd dent as a 'badge of honour' - you won;'t gain anything from a regrind, except shortening the potential overall life of the machine.

If the bed does have tight/loose patches, I would suggest grinding, scraping is only as good as your ability to test the results, and the ability to make a pretty pattern is not the same as the ability to get a flat surface. I can't do the former, but I can more or less do the latter. This means I restrict my shaping to improving the fit of two surfaces where it can't be seen!

Neil

I'm no scraper, but here is my first stab at a reply. The experts may follow later.

1)

Dents and dings usually leave a raised surround at the point of damage. This does not justify scraping the whole bed. Careful stoning to remove the high spots may be all that is needed for these faults.

Machining is good, but inevitably some movement through removing the possibly work hardened skin may leave that last few microns of distortion. Getting both sides of a casting level and parallel is also close by machining, but not close enough. Perfection always costs more than 'that'll do'.

Lubrication retention on a properly scraped surface is better.

2)

Scraping may be only the last stage of other machining so, no, not really!

3)

Of course it takes skill, as well as loads of patience. It is not just a matter of making one surface flat - there are numerous decisions to be made regarding the whole job where there are surfaces that must be flat and in the correct plane to other flat surfaces. One surface alteration done wrongly can mess up the whole job.

Edited By not done it yet on 18/07/2017 22:17:39

Scrape a lathe bed - no ! It would need regrinding , turcite strips fitted to the carriage to replace the metal that has been removed then scrape the carriage to fit the reground bed .

You may have seen some machines that have had the dovetails supposedly scraped and they do have some flaking or chequering done to make them look scraped but not so .

There are some guys on youtube that have scraped the cross slide surfaces on thier lathe or thier mill table surface and it is just a wank feature that does nothing to improve the machine .

I have scraped the dovetails on one of my Chinese mills to fix a tight spot and it was a PIA !

If you want to try scraping get hold of an old cast angle plate and re machine it then scrape that , if you stuff it up you are not losing anything as you can always re machine it and start again .

Ian.

If you suffer from arthritis in your hands then scraping will be a qiuckly passing fad i can tell you !

Hi,

Learning to hand scrape is relatively straight forward. Knowing what and where to scrape and how much to take off is the key.

I would recommend to start with learning to scrape flat. Then on to the 20 PPI (point per inch) 50% bearing and then onto 40 PPI. An old cast iron surface plate or angle plate are perfect starter projects. The angle plate would then allow you to learn scraping for alignment. Once your comfortable with 40 PPI then on to making your tooling that you will need to do a machine rebuild, e.g. straight edges, dovetail straight edges etc. If you really want to go to town get 3 old surface plates and turn them all in to master references but please do not do that unless you have lots of time available. much easier to have a known as good as you can get granite surface plate.

To get started you will need:

1. Hand scraper -- which you can make yourself. Personally I like a little spring in it as this cuts down on the effort considerably.

2. Blades -- you can make from carbide blanks silver soldered onto a bit of mild steel. I don't see the point of messing with old files. If your serious just start with carbide as it will save you time in the long run.

3. A means to radius and sharpen the blades. E.g. a 1200 grit diamond lap, for cast iron start on 5 deg negative rack and try it.

4. A reference surface plate

5. Some blue

For the hobbyist it is perfectly acceptable to scrape a lathe bed. However it is not possible to scrape a hardened bed which would indeed need sending out for grinding. I am not a myford lathe owner nor expert so I do not know if your model had a hardened bed or not. others will know. For a myford 7 lathe the bed design is pretty straight forward so it would not be too difficult a job you would just need a large enough surface plate.

There are lots of videos on youtube and some are excellent but some are not showing best practice, so be careful.

Steve

Dings and dents are nothing to worry about. Careful dressing with a few strokes of a flat smooth file will fix that. Not to remove the dent but to remove the high spot thrown up by the metal displaced from the dent.

You can measure the actual wear on a Myford bed quite easily with a micrometer. Most of the wear is usually six inches or so from the left hand end of the front shear. Measure the vertical thickness at the unworn right hand end of the front shear and compare it with the measurement of the high wear area. Myford specifies in one of their old brochures on reconditioned lathes that five thou of wear in that area is acceptable. More than that is cause for concern. (Which means in the home workshop you could probably get away with a bit more.) Likewise, measure the horizontal width of the front shear at the right hand end and the high wear area and compare. You will need a 1 to 2" micrometer for that.

Yes, scraping of machine tools is a highly skilled job and not really worth considering for a beginner if their lathe is at all useable in current condition. It's easy enough to learn how to make a nice looking scraper pattern on a surface, but getting that surface flat and true to suitable tolerances is a different matter.

Good advice from Hopper above CCB - old tools benefit most from a good clean and careful adjustment. That's what mine have received - and the rest is up to you. Get to know them before leaping in.

If you do want to learn scraping, then a small project is the place to start and if you muck it up (or run out of patience) then it won't matter so much.

Steve mentioned YouTube and the best on scraping I've seen recently is by Stefan Gotteswinter (always a very good watch) who recently put up two videos on the subject. You can find them here:

https://www.youtube.com/watch?v=QJXqHpSh3SE

But listen to Hopper and leave scraping off your ML7 "to-do" list for now....

Regards,

IanT

I'm a sucker for old engineering books and the history of engineering technique. Scraping has long intrigued me and I've come to some conclusions about it. They may be wrong! But, so far, my notions do fit with what the other posters have said.

Here goes:

• As a way of making a flat surface, scraping is long obsolete. It's been replaced by grinding. Ordinary grinding produces good results and where very high accuracy is required lapping and super-finishing are used. A hand-scraped surface plate will 'wring' to another flat surface in the same way gauge blocks are stuck together. This effect isn't wanted on a lathe bed!
• On plain bearings, hand scraping was used for a different purpose - to improve lubrication. Lathe bed-ways are a good example. The technique is rather different to that used to scrape a flat surface. Instead, an already flat bearing surface is carefully scraped to create between 12 and 30 evenly spaced high-points per square inch. Oil sits in the valleys and lubricates the high-points when the slide is moved. This type of scraping is, I think, more skilled than simply making a flat. For example, if the valleys are slightly too deep, they trap swarf and the bed will wear rapidly. As skilled fitting is expensive and perhaps 'hit and miss', the need to hand-scrape machine tools has been mostly designed out (thinks I). For example, on lathes, prismatic beds have replaced flat beds. The move away from hand-scraping for lubrication certainly predates WW2. There are probably exceptions, but I doubt that hand-scraping features much on modern kit.
• Being expensive, hand scraping has become associated with 'quality'. I've seen what looks like hand scraping on cheap tools. I think the effect was produced by a machine and am not convinced it's functional. Being a suspicious old Hector, I think it's probably only there to look good, like Boy Racer stripes on an old banger.

Happy to be told this is balony!

Dave

Edited By SillyOldDuffer on 19/07/2017 09:58:09

Well here is my two pennorth. I have done scraping in the past, but I have only seriously started quite recently. I have more or less got my 18" x12" cast iron surface plate flat with respect to a good 24" x 24" plate. I am not quite there, but another session should see me done.

If you are methodical and don't mind spending time on the job, then it is really very easy to do, so pay no heed to those that say it takes a lifetime to get the skills required!

Now trying to scrap a worn Myford bed flat, is a whole different ball park. You will need a large witness plate and the moving that over a worn surface is going to be a nightmare. As other contributors have said you will need extra equipment. I am not saying that it cannot be done, but I certainly would not even think of doing such a project. It might cost a bit, but get it surfaced ground, you won't regret it.

Andrew.

Here you go:

**LINK**

**LINK**

**LINK**

The table on my milling machine was reground just before I bought it, possibly by the company in the last of these links - a superb bit of work, and I can't detect any noticeable errors in it with the measuring equipment I have available.

If the £170 figure given in the first link is anything like the current price for a Myford I personally wouldn't need to think for very long on whether I should do the job myself.

Thanks all that is all very useful.

For the record Slideway Services Brian quoted £160 for a full ML7 bed regrind, so slightly cheaper

Edited By choochoo_baloo on 19/07/2017 18:35:26