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KB'S TOOLS AND REPAIR

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(905)-685-6000

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kbtools@bellnet.ca

BRIDGEPORT MILLING MACHINE REBUILD – PART III

MEASUREMENTS

The dovetail flats need to be explored. The knee runs primarily on the low end of the base, so expect to see wear marks. The flaking and scraping marks will probably be more evident at the top of the base. With a set of depth micrometers, you can measure the distance from the newly scraped datum to each dovetail flat, record the measurements. Don’t be afraid to take alot of measurements over the length as well as left and right. This will provide  a more accurate picture of the surfaces. The Starret precision level is placed on each dovetail flat to check for parallelism to the datum. It should be set at one end and a reading recorded, next move the level six inches forward, and record the next reading. Progress down the length, then check the other side in the same manner. It is very important to keep the level oriented the same way from here on out. The reason for this is to avoid errors, if you take the level and rotate it 180* you may get a different reading, depending on how well the level is set up. Always place the level in the same direction on the surface you are working on, unless you have taken the time to set up the level. Next, take a set of 1-2-3 blocks,  put one on each side of the dovetail flats,and placing the level on top of them. This will give you an overall view of the direction the flats are running in. Check at a number of locations along the length of the base, and record the readings.

MEASURE FROM THE DATUM TO THE DOVETAIL FLAT

 

MEASURE TO THE OUTSIDE OF THE FLAT

 

CHECKING THE FLATS FOR PARALLEL TO THE DATUM

 

MEASURING USING 1-2-3 BLOCKS AND STARRET LEVEL

 

BRIDGEPORT MILLING MACHINE REBUILD -PART IV

TOOLS

For those that are new to hand scraping, you will have to add a few tools to the collection. All the tools required to hand scrape can be bought new or if you search the Internet (eBay or other sites), most can be found used. Be selective and patient, but be willing to pay a fair price for a good tool.

 SURFACE PLATE

A granite surface plate is high on the priority list. This is one area of great importance. Surface plates are graded by the manufactures according to set standards.The Starret web site has great information on surface plates and is worth looking at. There are a number of used plates out there, If there is no calibration sticker with a date you should be careful about purchasing it. You can also get the surface plate calibrated if needed. The higher the grade the better. I purchased a used 24″x36″ Collins Micro Flat black granite plate that was re-qualified and  had a calibration tag that stated it was .0001 total flatness. I was sceptical and the seller agreed I could return the surface plate if I was not happy with it. The surface plate turned out to be a keeper. It should be noted surface plates should have mounting pads glued to the underside. This is what the plate sits on when it was qualified at the factory, and these pads are what the surface plate sits on when put onto a stand. A stand with adjustable feet will allow you to level it.

COLLINS MICRO FLAT

STRAIGHT EDGE

The straight edge or master is a cast iron flat that will need to be scraped to the surface plate. There are a number of shapes and sizes that are used. The Camel back shaped masters are more stable because of the arch design, however prism shapes work well for dovetails and angles. Straight edges can be purchased new, used or made from cast iron ,preferably Durabar.The straight edge is used to show the high and low points when scraping the machine ways. Ideally the surface plate should be used as the master, but because of its size and shape, it would be almost impossible to spot the ways. A well scraped straight edge will act as the new surface plate. The straight edge will distort with heat or cooling, so they should be checked and reworked if need on a regular basis. If a master is slightly distorted, the picture it produces on the machine ways will also be distorted. Most straight edges will have wooden handles because even body heat from holding the straight edge will cause the master to move.

Camel Back Straight Edge

 

BIAX

The Biax power scraper makes life easy. Scraping using a hand scraper takes a lot of energy and is tough on the body. Using a power scraper removes the physical motion need by a hand scraper. Both have their place when scraping, and it should be noted a simple hand scraper  is a lot more affordable and will do exactly what a power scraper does. The quality of the scraped surface has more to do with the individual then the tool.

The Biax Power Scraper

BITS AND PIECES

Altering and developing tools for a rebuild is not uncommon. In this case, I wanted to check the Flats of the base to one another. I started out using a Starret surface gauge with a .0001 test indicator and quickly ran into discrepancy’s in the readings resulting from the sag in the rods that were extended from one flat to the other. The solution was to use a Mitutoyo mag base with larger diameter rods, mounted to a cast iron block, which help to eliminate the rod sag and provided a nice stable base. The cast iron block was a leftover part from a Standard Modern lathe, actually I had three of these blocks. The flat surfaces of the blocks are 2″x3″ and were scraped to the surface plate. The opposite sides were then machined and ground parallel to the scraped surface making all three blocks the same dimensionally. The next tool that I need to make is a copy of a KingWay Alignment Tool, but more on that later.

CAST IRON SETUP BLOCKS

 

MAG BASE ON THE BLOCK WITH A .0001 INDICATOR

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