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Fasttrack
01-04-2010, 06:41 PM
I'm got back to school and reunited with my camera/pc cord that I left behind, so I thought I would post a couple of threads about my scraping attempts over Christmas break.

First up is scraping what was going to be a "master" for the dovetails on my shaper compound. The first day of break, I was able to score a bunch of "junk" - including a scraper and a block of cast iron that was about 4" by 4" by 2".

Pictures of the junk (that's a one ton Dake arbor press over there...)
http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010649.jpg

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010650.jpg

So the first step was to determine the angle of the dovetails so I could make a "blank" that I could scrape in. You can see the scraper that came with the junk in this photo (also, notice the block of cast iron and some sharpening stones in different grits - all from the pile of junk)

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010651.jpg

Truing up the sides in my little Smithy since I was away from all of my "real" machines :-(

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010664.jpg

Fasttrack
01-04-2010, 06:42 PM
To save time, I cut the piece on my bandsaw.

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010666.jpg

Here is the piece after face-milling the angle. I didn't really know what I was doing and was aiming for 55 degrees on the dot but I decided to cut it a couple of degrees less so I could "rock" it upwards to spot the dovetail.

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010669.jpg

I actually ended up scraping in the smaller piece of the two shown in the first picture because it had to fit in a tight place...The master/straight edge has to fit into the dovetail more or less "flush" in order to avoid the large center section that houses a bronze bush bearing and the nut for the slide.

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010686.jpg
(Don't mind the blue - I was just playing around)

Here is the surface plate with some blue laid out. A couple of things I noticed regarding set-up. First, paper-towels are handy but you need to be extremely vigilant to keep flecks of towel fiber out of the blue. Second, the rubber J-roller from Menards (~$10) is worth the money! Finally, regarding the scraper itself: Make sure you get all the rust knocked off it so your spotting compound doesn't turn into a lapping compound! It took me a long time to get all the rust off and to properly sharpen the blade where there were no little pock marks that would cause scratches on the work surface (my first attempt had several scratch marks).

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010675.jpg

I smeared out the blue too heavy, so I just transferred what was on my roller to a clean area of the granite and worked that way. I'm not sure why the heavy blue looks like its contaminated with shavings... it wasn't.

Fasttrack
01-04-2010, 06:42 PM
I forgot to take pictures of the early cycles, but they went pretty well. The piece was already very nearly flat from the flycutting (technically face-milling, I suppose) so there wasn't much to do. As I continued scraping, I ran into two distinct problems.

1) The spots were so tiny and faint that they were very hard to see (i.e. poor contrast). I came up with what I thought was a fantastic idea - burnish the workpiece with a contrasting color. So here I am using some of my sister's oil paint.

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010689.jpg

Unfortunately, it didn't work. The linseed oil must have reacted with something in the high-spot blue because it turned it into a really thick and sticky mess, despite the fact that there was barely any yellow on the workpiece at all (just barely a noticeable haze).

So I came up with a better solution that actually worked very well since it was winter time and the work piece cold. I found that I could breath gently on the part and the condesation of my breath would haze the metal, so there was better contrast (light blue against flat gray, instead of a shiny surface that made it tough to discern the spots). This is probably a questionable practice, but it worked well for me.

http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010692.jpg
(notice the "hazy" gray color of the background - I breathed on the scraper, too. It's hazy as well.)

2) My scraper was too big! With the "coffee-can" radius on the blade, it became very difficult to control the scraper to scrape less than about 3/16". As the spots got smaller, I used a little "finger scraper". I just took a piece of HSS 1/2" wide and sharpened like an ordinary scraper, but with a much smaller radius. I then used my hands and fingers to manipulate it. It worked very well for such a small piece, but I want to make a proper holder for it to handle larger pieces. (It was a little bit hard on the fingers after a while). It can be seen in picture above in the corner.

Here is a close up:
http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010697.jpg
(that is an inch across)

And the finished product:
http://i108.photobucket.com/albums/n22/fasttrack237/Scraping/P1010700.jpg

This picture is a little bit misleading. In the end, the least number of bearing spots per inch that I counted was 38 and the most was 52 (yes I actually counted - Connelly says 30-35 is surface plate or gauge quality and I wanted to be sure I did it properly). Towards the end, I actually pulled out a loupe to see spots and get figured out how the surface was evolving. Counting was a painstaking proccess involving lots of squinting. Some of the spots were so small and so light that they were tought to discern. From a distance, it looked like a pretty even blue haze. I was pleased with the results, although a little bit concerned with the difference in surface quality - i.e. one side was 38 spots per inch and towards the other end, the density of spots per inch increased. Next time I will shoot for a more consistent result (and not 50!!)


The b*tch of it is that I decided 4" is way too short :-D ... so now I'm looking at buying 12" of CI to make a gib strip out of CI (my earlier reaplacement gib was machined from steel, but I didn't want to tackle scraping steel so soon) and also make a proper straightedge for these dovetails. More details about the shaper project, specifically, is soon to follow in a seperate thread!

I just have to say that scraping is loads of fun. I really appreciate all of the help and inspiration that I get from visiting this board. I remember some 5-6 years ago when I first bought my Smithy, having never before seen any of these tools in person. Back then, "includes 3/8 and 7/16 draw bar" and "comes with MT3 dead center" sounded exotic and exciting ;-)

Mcgyver
01-05-2010, 08:40 AM
BS, I only count 51 :D

Looks like you've made a lot of progress.....you are scraping to a very high standard, probably more than i'd have patience for... but its a function of you're still in honeymoon stage and the area is small :)

How have you scraped in the angle on the gauge, and how do you plan on scraping the angle on the 12" gauge?

On scraping dovetails, there's kind of two ways to come at it, at least that i know....one being the 55 degree master is used to spot both surfaces of a dovetail, the second being that the master is simply some angle less than 55 and is used to spot only one surface at a time of the dovetail. The angle is checked by a smaller gauage, say maybe 1/2 in long. The former is more front end work, but makes spot and scraping the dovetail easier...that's how i've done it.

the tricky part is getting the two surfaces of the gauge perfect, such that they are both flat and at the same angle, and not at a compound angle. i don't think it matters a hoot whether its 55 or 55.1, but whatever it is you want it perfectly consistent and to save work, as close to the existing as possible.

for making a 4" gauge, maybe you did it via a sine plate and indicator...the size is small enough. Get one side flat, then set up the sine plate and get the other side so a tenths indicator stays quiet.

Unless you've got a big sine plate, things are more difficult at 12". You are probably going to have to make gauges to make gauges. How i've done this is scrape a small wedge shape pefectly to 55, maybe 1/2" long. Use it scrape perfectly an interior 55 degree gauge. Take your 12" dovetail master gauge, saw mill file then scrape on side flat. then using the interior gauge, scrape spots one the ends of the second side to the correct angle. Using the surface plate scrape the balance of the second side down to the same level as the two pads. This is how to get two surfaces at a consistent angle to one another when they exceed the size that can be easiely be indicated with sine bars and surface plates. Clear as mud?

With the gauge complete, get the two horizontal surfaces of the dovetail coplaner, then scrape the angled surfaces spotting with the gauge such that a distance across two ground pins remains the same. That also needs to be done square to the end

The other point is, plan the sequence out such that you are using one machine element to scrap another. For example, maybe because of hte protrusion instead of starting with the part pictured, scrape in its mate first and use that mate to spot the pictured part?

Another consideration is stability. Cast iron is the best bet, but still has stress and can move. That piece you found might have sat for 50 years, whereas the piece of durabar you buy might have more stresses. Short of sending it out for stress relieving, the tool maker trick of altering between freezer and oven (when there's a roast in) might have some merit. I didn't bother on a current job, but checking. Be aware of it, if it seems like you're chasing your tail on scraping that might be factor . Harry mention "Meehanite SE" in a recent thread, not sure what the SE is but if one cast iron product was more stable than another, that would be a good choice

hope that helps,

beckley23
01-05-2010, 06:44 PM
It's just plain old Meehanite. If I typed Meehanite SE, that was an error on my part. I refer to my Series 60 Monarch as SE 60.
The Meehanite straight edge I made for the "Wreck" has been the least troublesome of my straight edges, as far as touching up goes.
Personnally, I forego the exact angularity when I do the dovetails. I scrape in one dovetail, and match its mate to it. It's a whole lot easier.
Nice scraping, but 50+ points??
Harry

Mcgyver
01-05-2010, 07:10 PM
Hi Harry.....i agree it doesn't matter what the angle is, so long as it stays the same, but the trick is getting two surfaces at the same angle over some distance....I'm thinking scraping a V way or making a dovetail spotting tool. As i described i get one flat, then with small angle gauges (scraped) create to pads along the second then scrape the second down to the two pads, using angle gauge to help determine where material has to come off. I'm curious .... is your approach the same way?

Fasttrack
01-05-2010, 07:17 PM
Hey Mcgyver - I have not scraped in the angle. That was my original intent, which is why I referred to it as a "master". Based on the advice that Forrest gave (and Beckley23 mentions) I decided that maybe my best route was to scrape the dovetail flat and parallel and then match the other dovetail to it, rather than be concerned with the exact angle.

If I do decide to scrape in the angle, I was intending to use a goofy setup (no sine plate for me, yet... :) ). You can tell me whether you think it will work... I was planning on making a base for my tenths indicator so that I can leave the indicator stationary on the granite plate and then slide the master along the base. That will ensure that the master remains the same distance from the indicator at all times (assuming I have a good surface to slide along - for this I was going to use a piece of drill rod) and I should be able to detect whether or not master tapers. I'm not concerned with the exact angle.

I thought about doing the other piece first, but I decided against for relatively weak reasons. I'm still not completely decided on the best order of operations to attack a shaper in. It doesn't help that I don't have access to the shaper, so I'm not sure what kind of condition other parts are in. I'm starting to think that I will be scraping in all of the bearing surfaces - table, "knee", ram, and the tool depth "compound". Connelly suggests to start with the compound on a lathe, so maybe I'm on the right track ... ... :D



Nice scraping, but 50+ points??
Harry

Thank you! Like Mcgyver says, it was due to the fact that I was still in the "honeymoon stage" and because it was a small area to start with. It was a pleasent surprise when I decided to count it and determined that there were more than 35 spots. I was a little bit skeptical at first, but 50 spots per inch corresponds to spots that are roughly 1/8" by 1/8" (that's an area of ~0.016) so I guess it is reasonable. The spots were very tiny towards one end. The close up shot is the part where I counted 30 some odd. I dunno... :o

Oh, also my scraper was not very sharp. I felt like I was "polishing" off high spots instead of scraping. When I started working on my shaper parts, I resharpened the scraper and now it will really bite if I want it to (which is good because I needed to remove a lot of material!)


Thanks for all of the input, guys. I really appreciate it. All of it is still about as "clear as mud" so I'm still trying to feel my way along. I was just going to order some generic ductile CI from "online metals" or "speedy metals" or one of those. Sounds like I should look for Meehanite, instead. I seem to recall some other folks mentioning its stability.

Mcgyver
01-05-2010, 08:13 PM
one of us is missing something.

lets define a dovetail as as being 8 surfaces....4 on one piece and 4 on its mate. I fully agree use one part to scrape the other. So now there are four that we have to figure out. lets look at just 1/2 the one piece now, two planes that need to be flat and x degrees between them. what x is doesn't matter, what matter is that its X.0000 all the way along the dovetail, agreed?

How to accomplish this. Two ways i'm aware of.

1) create a spotting tool slightly more acute than X and scrape one surface. The angle is only to facility clearance into the dovetail and get one surface at a time flat. You need a second gauge, a small wedge shape at X degrees. It it only needs to be 1/2" wide. I use a sine bar and an indicator to scrape this as i want a simple angle (not compound, ie the two faces are square to the sides). you scrape one face with spotting tool and then the second, the second being done with the flat reference and the angle gauge. this method is imo a pita, but requires less up front work

2) make a dovetail spotting that has two surfaces flat and at the angle over their length. It was creating this tool that i was describing above. The best way is make the wedge, from the wedge make an interior angle gauge then use the interor angle gauge to make the dovetail spotting tool. The two surface dovetail spotting gets the dovetail ways flat and at and the right angle

btw, the sine bar/plate stuff is nice, but its main value is in preventing a compound angle, as stated that exact degrees don't much matter. Therefor you could just as easily bolt a parallel to an angle plate. Put the wedge on top of it and slide a 10th's indicator over the top (held in a surface gauge) and scrape until there is no movement. (scrape flat, notice where its high with the indicator, concentrate scraping on that side etc....done in conjunction with surface plate so it stays flat)

going with approach #2, to get the first piece done (4 surfaces), proceed as post above....get two coplaner etc.

getting stuff flat with scraping is relatively easy....the challenges come from figuring out how to get these flat planes in the correct arrangement with each other over a distance. Somehow, either directly or via the spotting tool you have to scrape two planes X.0000 degrees from each other over 12"...the earlier post just described how i've done it, I waiting to be pleasantly surprised with all the easier ways i didn't think of :)

Fasttrack
01-05-2010, 08:54 PM
Ahh - you were very polite in saying "one of us is missing something"; non-accusatory, as it were... :)

I was missing something, alright. I think I've got my head wrapped around it, now. Still have lots to learn! Unfortunately, all my shaper parts and scraping goodies are back at home. Soon, though, I'll be headed off to grad school and I've been looking at buying a small house with a garage. I'll finely be able to have all my machines and tools in one place!!

pcarpenter
01-06-2010, 05:59 PM
I think I understood at one point, McGyver that you were saying that you could scrape one surface to fit another. Then later on it sounded like you were saying that you must have a master that established the angle. With angles already roughed in for you by virtue of the fact that you are working on a once-correctly finished machine tool, here is what I did:

What I was tought to do was to scrape the flat faces of the dovetail flat and in plane with one another. If you don't have a lot to take off, this will be easy to maintain (roughly) by taking the same number cutting passes on each side. The next step is to scrape the adjoining angled dovetail surfaces flat and check the planar relationship along their length using pins and a micrometer (this was a male dovetail in my case so you could mic around the pins held into the dovetail. If the flat portions of the dovetail were indeed in plane with one another, the only source of variation would be because the angled side of the dovetail varied. The absolute angle mattered not...only that it was consistent along its length on each side. If one side was 55degrees and the other ended up 55degrees 42 minutes...that's not a huge deal...you will scrape the mating part to fit.

The angle is not so critical because the next step was to scrape the mating dovetails to fit, using the newly finished dovetail way surface as your master. In my case, scraping the saddle to fit the previously scraped knee ways on a Bridgeport mill. If I had screwed up the angle on a dovetail way surface such that one side was slightly different than the other, it didn't matter as long as I made the mating part match.

This fit's with Tom's scheme of having a slightly more acute angle on his master (for clearance). You are only using that angled face as a way of "reaching in there" without having your scraping master touch on both sides.

Paul

oldtiffie
01-06-2010, 06:27 PM
I have no problem with the scraping and angles of each dove-tail in isolation.

As there are two dove-tails and neglecting the gib for the moment those dove-tails will have to be very accurately parallel to each other else you will have a "wedge" effect.

The gib is another but not unrelated matter and requires high precision.

If the gib is "parallel" with several lateral adjusting screws (as on many mill and lathe slides) the issue will not be so important, in fact, in the case of the "parallel" gib, it is only necessary to scrape the side of the dove-tail that is opposite the gib on the "female" side but both sides of the dove-tail on the "male" side of the dove-tail slide.

If a tapered gib is involved - which seems to be the case here - (I can see what may be a gib adjusting screw at the top left) then a tapered gib will be necessary for its longitudinal adjustment.

A tapered gib requires two addition surfaces (the gib) as well as a female dove-tail that has non-parallel dove-tail angles to ensure that the inner face of the gib when adjusted is accurately parallel to the opposite side face of the male dove-tail which has parallel sides/dove-tail angles.

"Tapered gib" work, by its nature, involves compound angles.

On older machines I'd expect the gib taper to be about 1/8" per foot = 1/8":12" = 1:96 ~ 0.597 degrees ~ 35.8 minutes

There is a lot to consider here.

Forrest Addy
01-06-2010, 06:31 PM
There is an order and sequence to the scraping of a dovetail pair that reduces stock removal and keeps loss of geometry and axis shift to a minimum. There are favorite procedures and several are acceptable. Here's mine:

Conduct a survey of the dovetail surfaces and the relationsip to other reference sufaces that have to be brought back into geometrical compliance. DT flats to the swivel bottom for example. Determine which of the dovetail angles is least deteriorate and use that for reference for making a scraped prism in re-establichng the dovetail angles.

Plan your work then work your plan. Decide on a scraping plan. If you're not practiced it might be a good idea to write the plan down including free hand sketches of conditions as found.

to be completed later

Mcgyver
01-06-2010, 07:00 PM
I think I understood at one point, McGyver that you were saying that you could scrape one surface to fit another. Then later on it sounded like you were saying that you must have a master that established the angle.

as i said, the angle isn't important, only that it remains the same...that's why the angle gauge is necessary. you can use scraped part to match another, but not ad hoc, ie get all the geometry on one (the longer one) correct then use it to spot its mate.


What I was tought to do was to scrape the flat faces of the dovetail flat and in plane with one another.

agreed, that's what i wrote, get the horizontal surfaces coplaner is the first step


The next step is to scrape the adjoining angled dovetail surfaces flat and check the planar relationship along their length using pins and a micrometer (this was a male dovetail in my case so you could mic around the pins held into the dovetail. If the flat portions of the dovetail were indeed in plane with one another, the only source of variation would be because the angled side of the dovetail varied.

I don't think that's so, you could have a slight compound angle and end up with the same reading on the pins measured at each end but with a different angle at each end . If the angle is consistent AND the the distance across the pins are the same, we're good.




The angle is not so critical because the next step was to scrape the mating dovetails to fit, using the newly finished dovetail way surface as your master. In my case, scraping the saddle to fit the previously scraped knee ways on a Bridgeport mill. If I had screwed up the angle on a dovetail way surface such that one side was slightly different than the other, it didn't matter as long as I made the mating part match.

It doesn't matter that one is different from the other, agreed. BUT you have to get each them to be the same over their length .....which means you're either using a gauge or a dovetail spotting tool with the angle in place, so they end up the same just because they were derived from the same gauge...but there is nothing in their function such that the need to be the same


This fit's with Tom's scheme of having a slightly more acute angle on his master (for clearance). You are only using that angled face as a way of "reaching in there" without having your scraping master touch on both sides.

That was the #1 of two approaches i outlined. My preference is method 2 where the spotting tool has two scraped surfaces in the correct relationship. I quickly outlined in a previous post the methodology to getting two surfaces at exactly the same simple angle over a distance ....you can do it with a one surface spotting tool and angle gauge but its so restricted inside the dovetail that i find it much easier to establish a consistent angle betweent the planes on the more accessible dovetail spotting tool.

I don't think there's a right and wrong that the last point, just personal preference. If the dovetail is small however, I think the way i do it is preferable for the additional reason that it can be difficult to accurately spot the narrow surface of a small dovetail (ie 1/4" angle surface)

Really though, its pay me now or pay me latter. The angle needs to be the same over the length of the dovetail

OT, a tapered gib does add to things, my remarks are based on a simple straight gib. This is something i haven't done but I'd guess it was the same general approach, after everthing else is done rough out and scrape in gib to fit between the two castings, no?

beckley23
01-06-2010, 07:44 PM
Forrest makes a very good point about planning out the scraping sequence. Think it out very carefully. When I first decided to scrape the 12" CK in "Reconditioning a Lathe-Revisited" that appeared in HSM in 1984, I had thought about the bed sequence for years prior. I partially tested out the sequence on a 30" 10EE that I bought in 2001. It didn't need a full reconditioning, in fact the bed was in pretty good shape, and just needed a touch up. What I learned from that experiment in late 2002, was that the sequence was easier than I expected, if great care was used in selecting the reference section of the way face to be spotted, and if rigid monitoring was employed. I've used the same sequence on the CK, the wreck in "Wreck" Update, and the inside face of the front V way of the SE60 in Another New Toy, both in the Monarch Forum of PM. I've had no regrets. I don't recommend this for a newbie, it is a bit risky, and very tedious.
I didn't explain the sequence for the cross slide scraping in either topic, but they are essentually the same. These 2 lathes have very long cross slides, approx 90% of the length of the ways. I thought the cross slides would make good straight edges for spotting the ways, and that's how I solved a difficult problem in making sure the flat cross slide ways were being scraped parallel. The cross slide's flat slides were scraped first, spotting on a surface plate, the flat slides were then used to spot both flat ways at the same time.
In MTR, Connelly references off the cross feed screw, or a substitute, to monitor the parallelism of both the flat and dovetail ways. These surfaces on both the "Wreck" and SE60 were in very good shape, basically needing to be touched up, and I dispensed with the MTR monitoring. The one thing to watch out for is the nut alignment, and there are some work arounds if the displacement is excessive. I know I did some for the CK, the SE 60 is OK, and I haven't gotten that far on the "Wreck", yet. That will happen when I get the TA remounted. The only other issues are with the tapered gib, and I generally wind up shimming them on the static side. Occassionally the amount of material removed by the wear and scraping is so much that a new gib is needed, or I'll epoxy Multifil 426 to the dynamic side, and if it is really excessive the guiding dovetail slide will get the Multifil treatment also, which if IRCC, is what I did on the CK, just to get the nut "centered".
So, have a plan. There are a lot of surprises that come up.
Harry

Fasttrack
01-06-2010, 08:14 PM
I don't think that's so, you could have a slight compound angle and end up with the same reading on the pins measured at each end but with a different angle at each end . If the angle is consistent AND the the distance across the pins are the same, we're good.


It doesn't matter that one is different from the other, agreed. BUT you have to get each them to be the same over their length .....which means you're either using a gauge or a dovetail spotting tool with the angle in place, so they end up the same just because they were derived from the same gauge...but there is nothing in their function such that the need to be the same




Hmm... I would make a good politician; I'm sort of wishy-washy on this subject. I'm starting to come around to my original way of thinking :D


What you are calling a compound angle might be 55* at the top of the slide and 55.2* at the bottom of the slide, correct? The only way to do this is to "twist" the dovetail face or two make the two angled faces non-parallel.

What you are describing (I think) is what Connelly calls "wind" and as long as your straight edge is longer than the dovetails, you shouldn't have to worry about this. You can scrape the angled section of the dovetail to be a "perfectly" flat plane that is at some angle WRT the horizontal part of the dovetail. By running a piece of drill rod along the length of the dovetail and measuring the distances, you are testing to make sure the planes remain parallel.


I dunno ... maybe I'm still not picturing this quite right ...

Re: A Plan

Yes! I need a plan. Unfortunately, I don't know enough about scraping or, indeed, about the shaper to come up with a stead-fast plan. I expect this to be a very good learning experience! :)

Mcgyver
01-06-2010, 08:55 PM
The two horizontals are coplaner. One angled surface is perfect. you go to get the second perfect using only your one surfaced <55 spotting tool and mic'ing pins across the dovetail at each end.

I say its incorrect because if the angle of the second dovetail changed over its length AND the apex or line where the horizontal and angle surfaces meet (on the second dovetail) was not parallel to that of the first (in other words not square to the ends), the exact same distance across the pins could be read at each end while the dovetail is far from good.

ok, the ball just dropped on this.....I get what you're saying now, the above can't be true, else there'd be wind in the angle surface, ie it wouldn't pass the flat test. that makes sense...so i guess you can scrape them with pins :). As described, I've done it via making a two surfaced master and i'm sticking to my story that that's the easier route

lazlo
01-06-2010, 10:30 PM
You can scrape the angled section of the dovetail to be a "perfectly" flat plane that is at some angle WRT the horizontal part of the dovetail. By running a piece of drill rod along the length of the dovetail and measuring the distances, you are testing to make sure the planes remain parallel.

That's the way I've always read (from Connelly and Foundations): laying a pin in the dovetail and measuring with mikes. I'm not entirely following McGyver's method.

By the way Tom, it sounds like you've found this already, but this is all covered in chapter 9 of Connelly.

As far as scraping an arbitrary angle perpendicular to the base, couldn't you just scrape the base flat, mill and scrape the angle flat (as Tom's already done), then run a DTI across the prism while it's lying on a surface plate, measure how far out it is from being planar with the base, and adjust?

That's essentially how you scrape a right angle.

oldtiffie
01-06-2010, 11:03 PM
Not quite Lazlo.

Using (presumably two) rollers/pins and measuring over them is only OK if the faces of the dove-tails are flat and straight otherwise the rollers will or may either bridge any low spots or "rock" as they cross any high spots.

The rollers must be very true for roundness and straightness else they may give a "false" positive or negative reading.

A true roller and an accurate ball will soon give a good indicator of any "out of straight" and/or wear or high or low spots. The roller will bridge one side and act as a reference and the ball/s will soon find any irregularities along the lines of contact between the ball/s and the dove-tail. More readings with larger and smaller balls makes for a better data-set for planning purposes. Ideally the diameters of the balls and roller/s should be the same or similar but it really doesn't matter all that much.

"Outer" measurements should be taken with a micrometer over the roller and ball/s and "inner" measurements between the roller and ball/s should be taken with a good set of sliding parallel strips.

LittleMachineShop.com - search for item 2252 - ~US$30
http://littlemachineshop.com/products/product_view.php?ProductID=2552&category=

I'd be doing the ground-work on the surface plate (mill table, glass plate or granite) and then proceeding to the mill (fly-cutter) or the T&C or Universal Grinder (cup wheel) to get the bulk of the work done and then finish off with a light scrape if and as required.

If that job were mine I'd be looking to make a parallel gib (with new adjusting screws) and forget about (OK - dodge) the tapered gib altogether as it is a PITA - but is "do-able" - as I can quite easily do without the soul-destroying self-flagellation that it entails (to me anyway).
http://en.wikipedia.org/wiki/Flagellation

lazlo
01-07-2010, 09:31 AM
Not quite Lazlo.

The rollers must be very true for roundness and straightness else they may give a "false" positive or negative reading.

Good point Tiff. Tom: make sure your pin gauges are round :rolleyes:

pcarpenter
01-07-2010, 08:13 PM
I guess my point was that if the flat way and the adjoining angled way surface are both scraped such that you have bearing points all along their length (flat and planar as I called it before) then there is no ability to have a compound angle, wind (twist) etc. and this is what then allows you to use pins for checking the relationship of the angled surface to the flat one.

More important in my opinion is what Connelly calls "scraping down". It's ingrained in my mind because I let my mentor con me into ignoring it...and that was a costly mistake. It amounts to finding the shortest path to put the way surfaces back where they were. In scraping the belly out of worn doevetail ways, it's not too hard to maintain the same planar relationship by using the initial references at the ends of the worn way surfaces. If it was scraped correctly once, then a plane is already established by these unworn areas and the process of scraping back in amounts to evenly lowering this plane until you get bearing along the full length. This will be the quickest way back to flat for either a flat or angled way surface. In my (admittedly limited) experience, getting things back to the way they were can happen very quickly since it involves the minimum cutting necessary.

On the contrary, if you start with an angle master, then you are in a way ignoring the original angles that were there and saying "I want this angle to match my angle master, and not what was there before". The two ought to be the same in the ideal but probably not that perfect in reality.

Paul

lazlo
01-07-2010, 08:47 PM
On the contrary, if you start with an angle master, then you are in a way ignoring the original angles that were there and saying "I want this angle to match my angle master, and not what was there before". The two ought to be the same in the ideal but probably not that perfect in reality.

That's true with McGyver's angle master, but what Tom is making is the angle-gauge described in Connelly: two flat surfaces with some arbitrary angle < the angle of the dovetail. So you spot it by wedging it in the corner of the dovetail, and rocking it up into the top way. So as long as the angled surface is true to the base, you shouldn't be changing any alignment.

The typical manifestation of an angle gauge are the two surfaces on a camelback scraping master:

http://www.machinerepair.com/Tools_files/droppedImage.jpg

By the way, my previous post was agreeing with your measurement over the pins technique :)

pcarpenter
01-07-2010, 08:53 PM
Sorry-- my post was not just in reply to yours...but it did come just after yours. I guess I was trying to explain why the pin measurement is a valid way of testing the relationship of the two way surfaces and clarify that if the two surfaces are indeed scraped to be planar, there should be no chance of the pins being an invalid method of measurement.

If a master like Mcgyver was proposing is used, then both surfaces are scraped to the same relationship as the two faces of the master. This makes for a lot more work on a piece where some angles have already been established.

Paul

lazlo
01-07-2010, 08:57 PM
If a master like Mcgyver was proposing is used, then both surfaces are scraped to the same relationship as the two faces of the master. This makes for a lot more work on a piece where some angles have already been established.

Agreed. I saw that kind of angle-gauge on Pete Verbree's ("Shapeaholic") web page . He had a long write-up on it, but I can't seem to find his page any more.

Fasttrack
01-07-2010, 09:10 PM
Sorry-- my post was not just in reply to yours...but it did come just after yours. I guess I was trying to explain why the pin measurement is a valid way of testing the relationship of the two way surfaces and clarify that if the two surfaces are indeed scraped to be planar, there should be no chance of the pins being an invalid method of measurement.

If a master like Mcgyver was proposing is used, then both surfaces are scraped to the same relationship as the two faces of the master. This makes for a lot more work on a piece where some angles have already been established.

Paul

:) See post 16. Mcgyver is on the same page.

Thanks for all the advice. Later tonight I'll post a thread about what I've done so far on my shaper and why I probably should've waited and what my new plan is. I'd appreciate all the insight you folks are willing to offer! ;)

Wish I had one of those camelback angle gauges.