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Way Alignment Tool



Email Jim


Way Alignment Tool
May 21, 2016

Back in 2010 when I was getting ready to scrape my import mill, I made a crude approximation of the King Way alignment tool. It used flat stock for the horizontal bar and only used a one vial 6" level that I had made using some cast iron and a Starrett 199 - 0.0005" per 12" resolution spirit vial. Around the same time, I also made a cross check level using two of the Starrett vials, but there was no easy way to attach it to the flat bar of the makeshift alignment tool. The tool helped with scraping in the mill, but I realized that I needed to make another one that was a little closer to the original King Way design. I shelved the project for another day. Six years later, that day has come. I have a scraping project coming up where a proper dovetail way alignment tool would be a big help.

Over the years, I have read a lot about the King Way alignment tool and have collected pictures of the King Way and some shop made copies. The tool is ingenuously simple. It uses a horizontal bar to hold the cross check level, two vertical bars to hold a ground sphere on one side and a tube with a slot on the other, and an arm to mount a dial test indicator (DTI). In use, the tube with the slot is placed on the dovetail or V ways, the ball has a ground ring placed beneath it and is positioned on the opposite ways. The cross check level is then set to level in both planes and the DTI is placed in contact with the way you want to measure for height or divergence from parallel. By sliding the tool along the ways, you get your readings.

Squaring up some cast iron blocks.
Cutting out some sections to save milling time.

I started the project by squaring up some cast iron blocks on the shaper. I then cut and milled the blocks so that holes could be bored at 90 to each other. The holes were reamed to 0.501" diameter and then a slot was milled with a slitting saw so that the 1/2" diameter ground bars could be clamped in the holders.

Reaming the holes to 0.501".
Progress so far.

The shape of each holder was refined a bit and threads were tapped so that the clamp could be tightened on the bar. If I had to do the job again, I would change the design of the two bar mounts so that the mounting point of the horizontal bar would be at the top of the mount that supports the vertical bar. This would have allowed me to make the level holder a bit shorter.

Refining the shape.
A little more progress

When the holders were finished, I gave them a couple coats of paint using rolled up paper to keep the paint out of the reamed holes.

Time for some paint.
Test fitting the tool on the lathe.

With the two holders completed, I set the tool up on my lathe so I could measure how wide the holder for the cross check level could be. While I wanted to be able to set up the tool on the tailstock ways of my small South Bend lathe, the closest I could get the upright bars with the level between them was about 3.5". The distance between the two inner ways of the SB are about 3.0" center to center. This means that I will have to mount the level to the outside of the uprights when working on the tailstock ways. I could have narrowed the level holder clamp, but I was concerned that the weight of the level would rotate on the horizontal bar. The original King Way tool gets around this by slotting the horizontal bar and using a thumb screw for the level holder that locates in the slot. I am using two screws to clamp the holder to the bar. So far, it seems to work well.

I need to measure the distance between the holders and how much clearance I have for the cross check level.
Rough milling the holder that will attach the cross check level to the horizontal bar.

When I made the cross check level, it was machined from a round of cast iron. It is 6" x 7.5" x 1.25" thick and it is pretty heavy. I was worried that if the T shaped leg of the level was centered on the horizontal bar and I used a short tube when testing bed ways, the whole tool would tip toward the leg on the long side of the level. My solution was to make the level holder able to be reversed and thus get the bar clamp closer to the balance point of the level. This worked out very well and even with the short 5.5" slotted tube, the alignment tool doesn't want to tip when I tried it on the lathe.

The level used on the King Way tool looks to weigh less than mine. From what I understand, it also uses 0.0003" per 12" vials. The bar clamp appears to be cast into the level base rather than being an add-on piece like my copy.

Test fitting the holder to the level. The level overhangs the holder by a lot on the right side.
I made the holder so it could be reversed. This moves the balance point a bit to the right.

Once I had the level holder machined and I was able to make sure that it was square with the level, I drilled and reamed a 0.501" hole for the cross bar. I then machined a slit so that the holder could be clamped to the bar. Last, I refined the shape of the holder and added a couple pockets in the sides so that the vertical bars of the tool could be moved closer together. The upright bars can be adjusted to accommodate ways from about 3.5" to 15" apart with the current horizontal bar while holding the level between the uprights. For checking ways that are closer together than 3.5", the level can be moved to sit outside the uprights.

Finish milling the holder. I also milled some pockets so that the two legs of the tool could slide closer together.
Checking to see how everything fits. I need longer vertical legs. This will help with the DTI arm placement.

When I built the cross check level, I ended up making typical vial adjusters after a couple of unsuccessful designs. I ended up with coarser threads than are generally used for this purpose. My last design used 8-32 studs and cone shaped nuts that fit into reamed and slightly beveled holes on the vial holder end caps. To raise one side of the vial, you loosen the top nut, then raise the lower nut, then lock the top nut back down. This was a little fiddly because the 8-32 threads lift and lower the vial more than the resolution of the vials with barely a fraction of a turn. It took some of time to get the level adjusted, but once it was adjusted, it seemed to stay put pretty well. After more than a year of storage, the bubbles still centered perfectly. Now that I was using the level on the alignment tool, I needed to be able to re-level the vials with each use of the tool. I also wanted the ability to adjust the vials more finely. To do this, I decided on using a differential screw adjuster on one side of the vial holder. I had a spare brass end cap I had made when I built the brass vial holders. For a proof of concept, I tapped this end cap for 1/4"-20 threads. For the adjuster, I used a 1/4"-20 bolt with 8-32 internal threads tapped in to fit on to the 8-32 studs. This allowed me to raise or lower one end the vial holder by 0.01875" per revolution of the bolt. Not a fine enough adjustment for the sensitivity of the 0.0005" per 12" resolution vials, but better than the 8-32 threads alone. The test worked out very well. I found that I could adjust the vial pretty easily.

To make the permanent adjusters, I ordered some 1/4"-28 threaded studs and a 1/4"-28 tap. The closer the thread count of the differential screws are to each other, the finer the adjustment. The 1/4"-28 and the internal 8-32 threads would give me 0.0045" height adjustment for every revolution of the adjuster. A tenth of a revolution on the adjuster would raise or lower the vial holder by about half a thousandth. Not a super-fine adjustment, but it should be sufficient. I turned and knurled some adjustment thumb screws from brass to top off the adjustment screws. To get both gross and fine adjustments, I turned an 8-32 adjuster for one side of the vial and use the differential screw on the other. One side for gross adjustment and the other side for fine adjustment. Though they're not shown in the picture below right, I ended up putting springs under each side of the vial holder end caps to help hold the vials to their adjustment. I have to say that the adjusters turned out to work as well as I had hoped they would. It is very easy to get the level into adjustment as long as I have the cross bar somewhat level.

Proof of concept for the differential adjustment screw. The 1/4"-20 thread will be changed to 1/4"-28 for the finished adjusters.
With the adjuster knobs made. I again set it up on the lathe to check its operation. I need to make a new slotted tube to fit the lathe's ways better.

I made up a new slotted tube from the only appropriately sized stock I had on hand, 1" schedule 40 steel pipe. I need to purchase some tube with a 1/4" wall thickness to make the proper part, but decided that making a slotted tube from the schedule 40 pipe would give me a chance to play with the tool and get some practice using it. I also need to find my shop made tool post grinder to grind the end diameters of the next tube I make. I haven't come across it since we moved into the new house and shop, but I still haven't unpacked all of the boxes yet.

With the level mounted outside the uprights, I am setting the vials to be level.
Due to the weight of the level, I needed to hang a little ballast on the horizontal bar to prevent the tool from tipping.

In the last two pictures, the new slotted tube has been machined. The center section of the slot in the tube has been relieved so that only the 1" sections at each end contact the ways. To get the mating surfaces of the ends of the tubes square with the ways, I put a coat of ink from a felt tipped marker on the four flats, then rubbed the tube against both some V and dovetail ways. I used a fine file on the area where the ink had been rubbed off until I had four surfaces that contacted flush with the ways. The process was very similar to scraping flat surfaces, only I used a file instead of a scraper. Before I aligned the tube's slot, I tapped four holes into the tube. Two for V ways and two for dovetail. Because the pipe is so thin, I didn't get much thread engagement for the 1/2"-13 threads I turned on the ground 1/2" O1 stock , but it will have to do until I get the proper thick walled tube. The extra hole for each position will allow me some choice in positioning the slotted tube to see what works best.

With the tool more or less complete, I set it up on my SB9 lathe to test it out. Since the tailstock ways on the workshop lathe are only about 3" apart, I needed to move the level to outside the uprights. Since this puts the weight of the level to one side, I needed to counter-weight the horizontal bar to keep the tool from tipping. Not the best procedure, but it seems to work OK.

For my test of the new tool, I will attempt to measure the wear of the saddle ways on my lathe. It should be good practice for the upcoming project. To make sure that I am getting true readings, I will first check and correct for any twist in the lathe bed. The tailstock ways are realatively unworn. The scraping that was done at the factory to dust off the planer marks when the ways were machined are still evident, so using the tailstock ways to check for twist should be pretty accurate. In the past, I have attempted to correct for any twist by turning collars on a long piece of stock, then shim the lathe bed until I was able to turn the collars to pretty close to the same diameter. I currently have a 0.002" shim on the operator's side of the lathe bed foot at the tailstock end. However, as some sage person once said, "Machine tools are made of rubber." Add the fact that this light lathe is mounted to a butcher block bench and there is no doubt that the twist of the bed could change with the seasons. I am looking forward to seeing how close I can get the lathe to being free of twist and then checking the lathe for wear.

Using the setup shown in the last two pictures, using no DTI and just reading the level bubbles, I checked the tailstock ways for twist. The readings I got made me scratch my head. With both vial bubbles centered at the headstock end, I moved the tool to the right about six inches. The bubble measuring the X axis, the direction that the top slide moves, showed three increments high on the flat way side. I slid it toward the tailstock another six inches. It was now showing two increments high. At the third six inch stop, or 18" from the headstock, the bubble was centered again. The vial for the Z axis, left to right along the ways, showed the bubble pretty close to centered at each stop. I set up the DTI to measure the outer angled flat of the front V way and repeated the test. The V way showed less than 0.0003" deviation over the 18". It showed a little wear about 6" from the spindle snout and 0 in front of the snout and after about 12" from the snout.

Apparently I have a hump in the ways closest to the operator. Three divisions of the Starrett 199 vials would be 0.0015" per 12". That seemed like a lot. I quit for the night and decided to give it some more thought. The next day, I repeated the test with the same results and then it dawned on me that I was using vials calibrated to measure 12" and I was actually measuring the rate of slope for ways 3" apart. Duh. So the hump is there, but it's not 0.0015", it's closer to 0.00035". To confirm my thoughts, I re-leveled my surface plate using my frame level (0.0002" per 10") and used a 0.100" and a 0.10025" gauge block under my best wide parallel with the frame level above it. The results from placing the gauge blocks 12" apart and 3" apart and measuring their respective slopes confirmed my thoughts. Sometimes I need to spend the extra time to confirm what I think I know.

I will have to remember that the distance between the slotted tube and the sphere determines the amount of rise or fall that is depicted by each increment on the spirit vial. As for the South Bend, while I would prefer no hump in the ways, 3 1/2 ten-thousandths is a lot better than a thousandth and a half. I doubt that I will do anything to try and correct this. I have learned to produce pretty accurate work on this lathe in spite any deficiencies it may have.  Knowing where it is inaccurate will help me to produce better work.

I have a couple old lathe beds that I will spend some time mapping out. I need some practice time with this tool before I start using it to help me scrape ways that are true.

Fager May 21, 2016