Angled straight edge

[Iain DownsParticipant @iaindowns78295]

I'm currently in the process of rather tediously scraping the ways on my micro mill.

It's quite likely this is an early sign of dementia as there is clearly a limit to what can be done with these tiny machines and I'm quite sure that the improvement won't be worth the manpower I'm putting into it!

However, I've started so I'll finish – and better to ruin this learning the ropes than something of more value … I'm kind of enjoying the learning process too,

I'm getting there (I think) with the flat surfaces, but soon have to tackle the dovetails. I seem to need two things for the dovetails, an angled straight edge and some way of measuring them. I've got some precision ground bar (from a scanner) which will do nicely for the dowels, but I haven't worked out how to measure them. My measuring tools have a precision of 0.01mm (a bit less for the DTI which is analog). WIll this suffice?

More difficult is a straight edge to get into the dovetails. I can't find one to buy which I can afford and I can't find any 45 degree cast iron bar which I could lap or scrape into something suitably flat.

I have thought about using some angle iron and scraping that, but I doubt it would have even the meagre accuracy I need.

Bear in mind that my mill is currently in bits and would be troubling to use to make a 45 degree on a bar of suitable size (a bit under 12 inches)…

I'd welcome any suggestions or recommendations.

Thanks

Iain

[Iain DownsParticipant @iaindowns78295]

[John McNamaraParticipant @johnmcnamara74883]

Hi Ian

I would highly recommend you look for a book Machine tool reconditioning by Edward FConnelly, it fully describes the process.

You may be able to pick up a secondhand copy via the net.

**LINK**

The wedge shaped straightedge for dovetails does not have to match the dovetail angle it is usually slightly smaller. You only work on one angle surface at a time.

Best made from scraped cast iron. Maybe you can source a piece and mill it to shape then scrape it yourself.

Regards
John

[Ady1Participant @ady1]

For accurate angles a half decent smartphone can be used as a digital angle measure, the one here is good to 0.1 degrees and free. Android App: Bubble Level by Antoine Vianey (free).

I used it to check the ways on my Drummond, the flat glass screen makes an ideal surface for accurate measuring

[Roger HeadParticipant @rogerhead16992]

Posted by John McNamara on 12/07/2016 00:29:35:

Hi Ian

I would highly recommend you look for a book Machine tool reconditioning by Edward FConnelly, it fully describes the process.

You may be able to pick up a secondhand copy via the net.

Ian, I found a djvu copy on the web some time ago, can't remember where or when. PM me if you would like a copy.

Roger

[John McNamaraParticipant @johnmcnamara74883]

Hi

I have the actual book. picked it up from the (wonderful) secondhand bookshop in Charlotte St Brisbane Queensland while on holiday a while back.

Well worth seeking out.

Regards
John

 

Edited By John McNamara on 12/07/2016 02:55:30

[Roger HeadParticipant @rogerhead16992]

Posted by John McNamara on 12/07/2016 02:53:32:

I have the actual book. …

Well worth seeking out.

I agree, John, nothing like having the real thing propped up on your knee in bed. But I'm afraid that our 2nd-hand bookshops around here tend to pulp fiction rather than anything remotely technical.

Roger

[Iain DownsParticipant @iaindowns78295]

Hi, John.

I've heard of the book, though 'Foundations of Mechanical Accuracy' has also been suggested. That one at least seems a little to advanced for my amateur needs, but perhaps the reconditioning book is more practical.

Obviously, I'd thought of making an angle, but I have have two issues; My mill is in bits and half scraped; I need an edge longer than the milling width of the mill which makes holding the raw bar a bit of a challenge. I was hoping for a short cut!

Ady1 – thanks for the information on the app – worth looking into. Unfortunately, I don't see any method of getting the phone into the dovetail directly. It's only 8 or so mm high – smaller than the width of a phone! I might see if I can find some thin glass to use as an extension. In any event I can see other applications.

Iain

[John McNamaraParticipant @johnmcnamara74883]

Hi Iain

Foundations of Mechanical Accuracy is indeed one of the great texts of the world dealing with extreme accuracy machine design. given enough time and three "as cast" surface plate castings you could generate three superbly flat within a few millionths of an inch surfaces, and then after making them you could make all the tooling you need using the plates as a reference to set up your mill. If only we had the time.

Connelly's book may be a better choice for hands on work. Or better still get both.

Maybe your best course of action would be to find a kindred spirit in your neck of the woods to mill down or grind the straightedge you require.

I also have a much older mill that needs attention and in preparation for the restoration I have been able to purchase secondhand a nice granite surface plate. it is well worth keeping an eye out for one. a surface plate, a hand scraper made from an old file and a tube of Prussian blue oil paint is all you need to make high precision tooling.

Regards
John

[Ketan SwaliParticipant @ketanswali79440]

Iain,

May I suggest you give me a ring before you get carried away with your CMD10.

By the way, the dovetails are 55 deg.

Ketan at ARC.

[Ketan SwaliParticipant @ketanswali79440]

Posted by John McNamara on 12/07/2016 13:06:54:a surface plate, a hand scraper made from an old file and a tube of Prussian blue oil paint is all you need to make high precision tooling.

Regards
John

John,

I would suggest that 'skill' is also an important point to be taken into consideration.

Scraping is a lost art and skill which takes a long time to achieve.

Ketan at ARC.

[John McNamaraParticipant @johnmcnamara74883]

Hi Ketan

Skill yes it does require it and the members of this forum are a highly skilled group.

Scraping is not a lost art, Take apart any high end 2016 built machining centre and you will find evidence of it. Even with the finest micron level grinding machines machine elements have to be scraped, sometimes to correct small errors other times to deliberately bow a surface to allow for the part sagging by its own weight. This is art assisting geometry for perfection in movement.

It is a pity the built to a price Asian machine builders with their access to low cost labour will not spend a little extra time "fitting" their machines. You have to wonder why they bother to fit hand wheels graduated in thousandths to the cross slides if the machine is not capable of that level of accuracy over the length of travel a common complaint discussed variously many times in this forum.

There are many well presented videos and discussions on the net, an invaluable resource for those that wish to learn the process. Yes it will take time, once learnt it is very empowering.

Regards
John

Edited By John McNamara on 13/07/2016 00:28:18

[John McNamaraParticipant @johnmcnamara74883]

Hi

I just found this set of videos on machine alignment. In this case a CNC mill I have not viewed them all but for someone working on improving a machine tool worth viewing.

**LINK**

Regards
John

[Anonymous]

Interesting videos, thanks. Even more interesting is that the machine uses linear ways, as do a lot of commercial CNC machines as far as I know. I can't imagine there being much point in scraping if one is using linear ways?

I suspect that the reason built to a price manufacturers don't 'fit' is simple economics. How many times do you see posts on here where the poster is contemplating buying an XYZ lathe, or mill, from supplier ABC or DEF? And one supplier is tuppence h'penny cheaper, so that determines the choice. So why increase the cost of manufacture?

I understand that Myford lathes were scraped and fitted, but it didn't do them any good. I wonder how many of those on here with a Myford bought it new from the factory?

Andrew

[Iain DownsParticipant @iaindowns78295]

I just wanted to publicly thank Ketan, who called me a couple of days ago and spent half an hour offering advice on how to practically tune up my mill based on their experience with their version of the same machine.

I should add that I'm barely a customer, having only purchased some spare parts and the odd cutter! Above and beyond the call of duty.

I think, at the moment, I'm going to re-assemble the mill so that I can cut a 55 degree prism to tune up the dovetails (after I take it apart again). Ketan's recommendation was essentially to lap them rather than scrape. I've got a couple of the ways considerably better (several dozen bearing points as opposed to 3…), but feel like a holiday before tackling the ways into the dovetails!

It's also about time I built something with the Mil….

I may have a go a something a bit more straightforward and less critical when I recover my scraping energy. A simple straight edge or plate.

I must say it's quite challenging picking this up. The videos on the web and the written stuff (including this list!) I've found offer apparently contradictory views on technique, scraper shape and so on. Perhaps one of the members with skills in this area (of whom there must be many) would be interested in offering a workshop. I'd be interested and would even (gasp!) consider paying. And that from a Yorkshireman.

Dedication indeed.

Many thanks as always for pointers and advice.

Iain

[Author]

Posts