It is important that you have no corners on the blade, as these can cut right through a hide and securing the blade to the bottom of a surface works well to keep down the accumulation of hair and hide on the tool. You may find a branch that works well for the handle or cut one out of some lumber. You may even wish to mount the blade at a 45 degree angle instead of the 90 degree angle shown. Of course you may use all stone tools in the entire process, if you wish to keep everything completely primitive or as in a survival situation where you have no choice. Now, all hair and epidermis must be scraped from hair side of hide.
Epidermis is that first layer of skin that contains the hair follicles.
All epidermis must be removed to produce a hide that is 'suede' on both sides, which is the Native American way of doing it. Otherwise you will be left with shiny spots that may not absorb the brains properly. All hair follicles can usually be removed by taking a 12 inch x 12 inch square and scraping about 35 times and moving to another square until you have completed scraping entire hair side of the hide provided the tool is very sharp, however, check anyway for any hair follicles, even when it seems you've removed all that shiny epidermis. If you have very good light you may cast a shadow with your hand and look very closely for tiny black spots indicating hair. Keep scraping until it's all gone.