Scraping and Struggling.

[Abratool]

Hi BT,

Been thinking about the problem of scraping three surfaces to come together at the same time, here is one approach, others with more scraping experience might have a better method, first, I wouldn't use the surface plate, since you are scraping to suit an existing part, then my thought is that, that should be your reference.

Using Stuart's idea of reversing using the spigot as the center of rotation should ensure that your bevelled sides are centered on the spigot. Which leave the problem of how to get close enough to scrape, I would take it slowly gradually increasing the bevel until you get down to a thou or so clearance at the top. I hope this sketch helps.



The central idea I want to convey is that it's better for stability that the three surfaces to be very slightly concave, than to have a high spot in the middle.

I see it as an exercise in patience.
You need to get into that Zen mind set for scraping.

Regards
Ray

Ray
Same thinking that I had. Please see my post on 31st Dec @9 52 am.
I think if the bevels were scraped down & say a feeler gauge was used for the last 1.5 thou or 2 thou to ensure the larger flat surface was getting close to its mate, then that would be as you have mentioned, better than trying to get a result with a surface plate.
The master or reference piece in this job is the finished mating piece that Bob already has.We know that piece is as good as one could wish for.
Once that small gap closes up as the bevel scraping proceeds, blue is applied & finish scraping achieved.
I think also on these jobs you have got to hold the tongue the right way...Zen mindset or something similiar.
regards
Bruce

[Pete F]

Ray, that's pretty much what I was suggesting above, I probably just didn't communicate it very well; scrape the flat surface, then the bevels to fit.

I would expect the bevels to come in to alignment together if carefully scraped. I don't see any reason they should wildly differ as they're both being scraped at the same time. However if concerned about keeping them central to the hole for the spigot, I think I'd turn up a plug with a flange on it to a close fit in that spigot hole, and mount an indicator to the plug. Sweep the dti to the bevels to ensure they're remaining central. Maybe I've misunderstood what is being made here.

Pete

Edit: I should add that's coming from somebody with very little scraping experience, and virtually none on scraping to alignment. So take the suggestion for what it's worth. It's just how I would approach the problem as I see it.

[Anorak Bob]

I'm getting real squirmy about this. The idea of scraping two bevels evenly to ensure concentricity while at the same time maintaining both parallelism and 60 degrees is pushing me well beyond my skill level. I know there are some who think this is a piece of but the only scraping I have done is the puerile example displayed earlier in this thread.

I spent considerable time yesterday realigning the mill table. I'm thinking of remachining the top flat section and cutting a 30mm wide set down as per the original base, then cutting one bevel and measuring by means of a pair of dowels, dovetail style, cut the second bevel. I can blue the thing up and see how bad it is. I have enough height in the block to repeat this a number of times.

Once again Boys, I appreciate your thoughts.

BT

[.RC.]

I'm getting real squirmy about this. The idea of scraping two bevels evenly to ensure concentricity while at the same time maintaining both parallelism and 60 degrees is pushing me well beyond my skill level.
BT

That is why you do it first, them machine everything else from there...

I actually can not see too much difficulty with the scraping you want to do...

Sounds to me you need to go to a scraping class.... Who knows what the future will bring there...

[Abratool]

Bob
There are some out here to use your words "Think its a piece of "
and it is, really, yes really.A damn good exercise in concentration.
Just narrow down the parameters, as mentioned in the various suggestions, & start "worrying it off".
It will all work, just take your time, & dont rush it, or get frustrated, as I frequently say there is no bus to catch.
regards
Bruce
ps.......I still like the idea of machining, then scraping the 2 bevels until the flat surface eliminates the light coming through & starts to see a bit of blue. The precision rollers to measure as you proceed would assist.

[Anorak Bob]

Stuart was correct about how bad the results would be if I machined off the scraped surface.

I'll refit and carefully tram the vertical head. Then I will have another go. I've removed about 0.5 mm, no big deal. That's a brand new, never used Clarkson slot drill. Obviously not intended for nice finishing.

[Abratool]

Bob
Now ,Bob........ lets get serious,..... this job is not all that hard......Really.
Maybe you need another drink of water at 3 am as per one of your previous messages a bit of water at that time of the morning does help!
May I suggest re reading Raygs comment of Jan2 @ 1.44 pm. For me as I read it..... it makes a lot of sense.
Here are my considered thought out suggestions, reconsidering raygs comments.....at this time of night around 10 .45 pm in the eastern state of NSW
Forget about trying to obtain flatness with a Clarkson cutter or hand scraping the flat surface to a surface plate, or any thing else about the flat surface..... Just forget it for the time being.
Machine the bevels or the 60 degree angles, so there is a thou & a half or 2 thou of clearance between the larger flat surfaces, use rollers or toolmakers buttons (on their sides) or dowels to have a predetermined dimension to work to , so that not too much is machined off.This can be calculated by using the same rollers as measuring tools off your finished Shaublin reference which is..... the only true reference.
All the rest are superfluous ,(Not needed)
You have the good equipment, centering microscopes, indicators etc after you achieve the above to follow through to completion.
Go !
,You can do it
regards
Bruce


Forget about trying to machine the flat surface with Clarkson cutters or trying to scrape it flat to surface plates.

[Anorak Bob]

Bob



Forget about trying to machine the flat surface with Clarkson cutters or trying to scrape it flat to surface plates.

After the failure of the horizontally mounted slot drill in creating a flat surface, I remounted the vertical head and spent considerable time tramming it. Refitted the PRESTO 1 5/8" end mill and had another go. The results displayed an even criss crossing of cuts. Ignore the set down section on the block, that's the result from using a 30mm slot drill and a faster feed.

I cut the bevel to size on one side then, progressively measuring using a pair of dowels, cut the second bevel. Sadly 0.02mm undersize. It's surprising how sloppy a fit it was with the dividing head fitted.

I refitted the end mill and very, very carefully remachined the upper flat surface, 0.01mm each cut, knocking the high spots off with a hard Arkansas stone and test fitting the head between cuts. Blued up, there is contact on all surfaces. With a 1um indicator measuring play at the end of a bar projecting 100mm beyond the spindle nose and with my bulk pressing down on the dividing head, there is 4um movement ( 0.00016" ). I don't know if the play is from a sloppy fit or from the head riding up on the bevels when twisted. I'll machine the tee slot next and find out.

Given my lack of knowledge and skill in the art of scraping, I'm happy to leave the fit as machined for the time being.

The perception will be that I ignored most of the advice proffered, but in doing so I discovered a bit more about my mill and it's capabilities.

My next challenge will be finding the center and finding out how to align the Hensoldt centering microscope to achieve the former.

BT

[RayG]

Hi BT,

Nicely done.. 4 microns, wow, that's an impressive bit of work..

Regards
Ray

[Anorak Bob]

Ray,

Luck would have been responsible for that result.

BT

[Stustoys]

Hi BT,
Looking great so far. I certainly wouldnt be losing sleep over 0.004mm just yet .

Stuart

[Michael G]

I'd certainly leave it at that for the moment - you have no relative movement between the parts so I'd suggest that scraping is optional

Michael

[Anorak Bob]

I'd certainly leave it at that for the moment - you have no relative movement between the parts so I'd suggest that scraping is optional

Michael

Well I must have got something right. I machined the tee slot this morning and clamped the head in place. With a non Schaublin W20 collet and a 1/2" test bar, a transfer punch that had less run out than anything else that came to hand, I set up a 1um indicator. At the spindle nose there was no needle movement. 90mm from the nose there was 5um TIR (0.0002"). I rotated the test bar to the mid position between the extremes of the run out and traversed the table the length of the bar. There was no discernable needle movement. I checked this a number of times with the same result. Switched to a 0.0001" DTI with the same results. I traversed the indicator along both the vertical and horizontal centerlines of the bar. Removed and reclamped the head on the base. Same results again. No bad for a 50 year old machine.

Now comes another challenge. Finding center. A thought had occurred that the centerline of the dividing head may not align with that of the factory swivel base given that the head ( and tailstock ) are scraped to fit the base. I had thought that I could use the Hensoldt to align the mill spindle with a W20 dead center collet mounted in the dividing head spindle. Sadly, there is insufficient room to install the scope.

My current thinking is to install a 10 mm bar in the dividing head and the same size bar in a collet chuck mounted in the vertical head. Using a loupe, bring them into contact , then wind the spindle over 10mm.

Any other suggestions?

BT

[Stustoys]

Hi BT.

Using a loupe, bring them into contact , then wind the spindle over 10mm.

I'd forget the loupe and use feeler gauge or shim. Using a loupe so see light between two round parts will drive you nuts I think its going to be a point contact. You could try both and see if they agree, also you could test from both sides.

Back the the shed for me.

Stuart

[Abratool]

Bob
I just got home from being away up north, fishing, catching mud crabs, & body boarding in the Yamba Surf. Also enjoying grandkids.
The first thing I looked up was how you were progressing & it was very pleasing to read your report. The blue looks to be in the right places & the machining is exceptional as the indicator reading has shown.
I do not think scraping will be needed, it is really good as it is.
Well done!
Bruce