Thread: Scraping and Struggling.

Hi BT,
I'm not sure if we are helping you bail or turning the water on harder?

I know I've asked this before some where but I cant find it.
I'm wondering again along the lines of RC.
How about you
rough the bevels
machine the tee slot
bolt it to the face plate and machine the spigot
make the base
scape the base parallel
scrape the bottom face of the table flat to the base
mount base and table on mill
fly cut one side of the top flat face.
rotate the table 180 degrees fly cut the other half
set up your bevel cutter
cut one side
(now for the fiddly part)
rotate 180 degree as near to exactly as you choose to get
cut the other bevel
repeat until you are happy with the size.

The 180 degree turns mean that you will be centered on the spigot and any errors in your table alignment will be halved(across the flat face) and at opposite ends. I think this would be easier to scrape in than if you machine it in one setting and make a wedge.

My dumbest idea ever?

Stuart

Stu,

Your sequence of events makes sense. The problem I have is that the fitting of my base to the Schaublin head is the last operation and the most risk ridden (for me). The scraping of the three surfaces, while at the same time maintaining concentricity, is a task I find daunting.

I would prefer to meet with disaster at this early stage rather than the end.

Bob.

Next thought -
(I hope you run out of problems before we run out of thoughts)
If you make up the base - even if just a piece of metal with just the spigot hole and bolt that to the mill table, you can use a DTI to get that concentric with the spindle. Truing the base up (making it parallel to the mill axis) should not be difficult as you would use the same technique as you do for aligning a vice. Using a combination of the table screws and the DTI (or an indicator) you should then be able to determine whether or not the sides are equidistant from the spigot. Any cyclic error on the table screws should be minimised as you will be turning the screw the same number of turns (although in different directions) for each measurement.

Thanks for the photos in your 11:19am post. It clarifies things a bit but also shows that the whole top surface does not have to be flat - just the bevels and a strip along side. On your base it's probably worth machining that bit that does not have to be flat down so that you can concentrate your efforts on the important bits.

Michael

Hi BT,
I'm struggling to see how you will be able to drill the hole between the bevels close enough* to the ensure alignment of the spigot.

I dont think you'd be able to wreak it while scraping, it will take you a long time to remove 1mm(?)
Still you can try it your way. If that doesnt work you'll likely only have to machine 0.5mm off to try it my way.

Stuart

*As always what is "close enough"?

Stu, Michael. Happy New Year.

Thanks for thinking about this when you should be doing other things. I'm having trouble typing. Peroni, 2.99 clear skin cab merlot and red Johnny don't mix real well.

I borrowed a center microscope and a beautifully ground angle plate from another forum member. Blued up the plate and placed it on the scraped surface. The results were that bad that I will remachine the surface tomorrow. A slot drill cut surface will be better than what I have managed. The centrer scope will allow me to accurately pick up an edge.

BT

Morning BT,
Happy New Year.
Hows the head? lol
You might be surprised how bad your freshly machined surface looks when spotted.

I've had another thought, How much adjustment is there in the Tee bolt clamping system? It might be good to machine the Tee slot deep so if you need a couple of goes to get the top face right you wont run out of adjustment?

Stuart

Bob
I have been impressed with the number of ideas feeding into your problem job.
There was an old saying in the tooling game, that sometimes difficult jobs can be "worried through"
I think your particular machining challenge falls into that category.
Even though I have been working on a timber staircase rebuilding job for the past 50 hours or so, at my home, your problem job is in the back of the mind.
This morning there was consideration of using precision steel rollers to measure the distance between the dovetails on your job, but as mentioned there is a wealth of knowlege, being sent to you.
All the best to you & all on the forum for 2012.
regards
Bruce

Good Morning Fellas.

The huge drink of water at 3am did the trick.

I do greatly appreciate the consideration and advice given to me by you all for what should be a simple little project. The pursuit of accuracy has proven to be quite a challenge. Attempting to match the accuracy of the original fixture is ambitious. Without the appropriate equipment, I imagine unattainable. I do need to acquire a surface plate, without one I'm wasting my time.

I will remove the workpiece and tram the table and spindle for starters. I'll also send GQ a message re his Czech special.

All the Best.
BT

Originally Posted by Anorak Bob

I do need to acquire a surface plate, without one I'm wasting my time.

Ah! In my suggestions I was assuming you had one Bob. Yes you need a surface plate. In a couple of months I expect to have one for sale

Pete

Originally Posted by Pete F

Ah! In my suggestions I was assuming you had one Bob. Yes you need a surface plate. In a couple of months I expect to have one for sale

Pete

I just hit the buy it now button for Gregory's Czech plate. I'm starting to see light on at the tunnel's end.

Thanks Pete.

BT

Originally Posted by Anorak Bob

I'm starting to see light on at the tunnel's end.

Thanks Pete.

BT

In my case, more often than not that light turns out to be a train!

Bob, the Carbatec granit plate I purchased just before the scraping course has proved invaluable to me. It's 9"x12" and not too heavy - and surprisingly accurate.
I can recommend that. It was $59.

Joe

Thank you Joe,

Sounds like a useful companion for the 400 x 500 plate Greg has. I will check it out.

BT

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