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How to use a curved engineer’s scraper

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Inked master shaft being placed into a bearing Unlike flat scrapers, curved scrapers are not used to make a surface flat. Instead they are used to achieve a very accurate fit between two curved surfaces, such as a cylinder and a bearing, or a bearing and a shaft.

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Engineers spotting ink used to highlight high spots within the bearing

Engineer’s spotting ink

This is used to highlight the areas on the workpiece that are causing a sticking point and need scraping.

There are many types of spotting ink that can be used in scraping, the most popular is Prussian Blue.

Small roller is used to roll an even layer of ink on the master shaft

Small roller

A small rubber roller is best to spread the ink, although the foam sort you would use in decorating can also be used. This is needed to roll a thin, even layer of the spotting ink.

Microfibre cloth is used to clean the master shaft

Microfibre cloth

The microfibre cloth lifts dirt from the surface of the workpiece, leaving it clean and ready to be scraped.

Felt tip pen is used to divide up the bearing into sections

Felt tip pen

A felt tip pen is used to divide and mark up the sections to be scraped between the oil grooves of a Babbit bearing.

Soft bristled brush is used to clean inside the bearing

Brush

You will need a soft-bristled brush to clean off the scraped metal from your workpiece.

Wonkee Donkee would use a toothbrush, You may find a small brush with bristles at a right angle to the handle, such as a tooth brush easier to use inside a bearing or cylinder.
Master shaft is used to transfer ink onto the high spots within the bearing

Master shaft

This is the shaft that will be fitted into the cylinder or bearing.

Curved scraper technique

How to hold a curved blade scraper Hold the curved scraper with your dominant hand at the top of the handle and the other at the base of the handle, as you would a large pepper grinder.
How to stand when scraping a bearing You should stand with your feet shoulders width apart with one foot in front of the other, facing the workpiece so you are able to look down the bearing you will be scraping.

You need to be able to see down the bearing to see the spotting ink marks that have to be scraped.

Action used with a curved blade scraper, Rotate the scraper with the other hand, Push the scraper with your dominant hand Push the scraper away from you with your dominant hand, whilst rotating the scraper blade with the other.
Direction of rotation used with a curved blade scraper, Rotate the scraper in the direction of the cutting edge in contact with the work piece The curved scraper blade should rest on the workpiece and be rotated towards the direction of the scraping edge in contact with the workpiece.

Babbit bearing scraping process

Inked master shaft being placed into a bearing Instead of using a reference plate, the shaft that is to be inserted into the bearing or cylinder is coated with the marking ink. As the shaft is pushed into the bearing or cylinder it leaves traces of the marking ink on all the contact areas (these are the equivalent of high spots).
Master shaft being cleaned; soft-bristled brush clearing away dirt from master shaft

Step 1 – Clean workpiece and master shaft

Begin by first checking that your workpiece and master shaft are clean.

Use the soft-bristled brush to clear away dirt and then wipe over both the master shaft and workpiece with a microfibre cloth.

Master shaft being inked

Step 2 – Ink shaft

Apply a couple of drops of spotting ink to the master shaft and use the roller to spread it out thinly and evenly over the surface.

Wonkee Donkee using a reference plate to get a thinner layer of ink, If you have a reference plate available some people prefer to roll out an area of spotting ink on it and then using the roller transfer some of this ink to the master shaft in order to get a thinner layer of spotting ink on the master shaft.
Inked master shaft being placed into a bearing

Step 3 – Position shaft in bearing

Place the inked master shaft into the bearing. Do not force the shaft into the bearing.

Rotate the shaft in the bearing in the direction it will turn

Step 4 – Rotate shaft

Rotate the shaft in the bearing in the direction the shaft will spin. Then remove the shaft from the bearing.

Oil grooves in bearing

Step 5 – Divide up bearing

Divide each section between the oil grooves up into six equal smaller size sections and mark them using a felt tip pen.

Divide up the bearing between the oil groves, Divide each section of the bearing up into 6 equal size sections with the felt tip pen This is how the bearing should look once the master shaft has been removed and the sections between the oil grooves divided up and marked with felt tip.
Contact points between the master shaft and the bearing, Sticking points in the bearing are highlighted by the spotting ink

Step 6 – Scrape contact points

The contact points between the master shaft and the bearing will be highlighted by the spotting ink.

Using a curved blade scraper Using the curved blade scraper, scrape the contact points.
Bearing being brushed clean

Step 7 – Clean inside bearing

Using the soft-bristled brush, clean the inside of the bearing or cylinder to remove any scraped metal or dirt. Then repeat steps 2, 3 and 4

Sections of the bearing that need scraping

Step 8 – Repeat scraping

If the felt tip pen marks are no longer visible, repeat step 5, then repeat steps 6 and 7 until 80% of the four middle sections between the oil grooves (highlighted in yellow) are highlighted by the spotting ink.

Areas near the oil groves that need more scraping

Step 9 – Scrape only outer sections

Once 80% of the middle four sections are highlighted with spotting ink, scrape only the outer two sections nearest the oil grooves.

Repeat steps 2-7 scraping only the outer two sections nearest the oil grooves (highlighted in blue) until there is not spotting ink visible in these areas.

Bearing after scraping is complete Once you reach this stage, the bearing should look something like this. All that is now left to be done is brush the inside of the bearing and wipe it clean with a microfibre cloth.
Why do you scrape all the contact points away from around the oil groves?

Why scrape all the contact points away from around the oil grooves?

By scraping away all of the contact points next to the oil grooves, oil dispersion around the bearing is improved. The 80% contact points between the oil grooves ensure the master shaft will be evenly supported within the bearing and so rotate true.