Scraping a drill press table

[Erik Brewster]

I decided I need a project in the garage that had lots of mindless effort and relatively little planning, so I scraped a cheap drill press (13" diameter) table flat.


I don't present this as a great idea for several reasons:
- I didn't need to be very flat
- It isn't the best drill press in town, so any accuracy improvement is likely lost on it
- I could have likely improved the drill press more in the same time doing something else
- It should have been remachined flatter before scraping, but scraping was kind of the point and my mill is sick.


What I did that worked well:
- The table is pretty flat now
- I didn't spend one cent (other than electricity)
- It was therapeutic to just be out there with the scraper
- I found that my scraper is at the end of its brush life and I will have to deal with that
- The biax allowed me to tackle more scraping than I would have ever done by hand.

Here is the starting point. I didn't measure the dip in the middle, but I would say it was between 0.005" - 0.010" deep in the middle.


Here is the end of day 1 (1 hour of scraping). I did some light scraping all over, but not enough. I'm using a long stroke (1/2"?) and really leaning on the scraper here. This is just roughing, while keeping track that I'm not creating a huge hole somewhere.


Here is the end of day 2 (1 more hour of scraping). I scraped some more in the middle. I found that the machined surface was a LOT harder than the scraped surface. Scraping through this not only removed the machining marks, but got to a uniform hardness. The outline is the low spot left to scrape.


Here is the end of day 3 (1 more hour of scraping). You can see that as I scrape more surface flat, it takes longer to dig down.


Here is the end of day 4 (3 more hours). There is a nice distribution of blue spots all over (there are some minor depressions in the middle). The spots are reasonably sized for the job.


Here is a 1 square inch hole in a paper to see that there are ~15 spots / in^2. I don't know how I would do less than that with a Biax without leaving a big hole somewhere and having any real spot size.


Here is a picture of the final result, with the blue cleaned off.


What did I learn?
- If you want some physical labor, scraping will do it for you.
- Don't drop your deburring stone - it will break in two
- Scraping isn't really that hard, if you follow Rich's method. Let's see if I can remember...
-- Pivot the part to make sure you have uniform contact when you think you do. This was a revelation to me the first time and really gives me confidence that I can trust the bluing pattern
-- Scrape individual scrapes. I admit that I am pretty lax on this, but follow the general concept, while scraping in a zig zag shape. When I'm finish scraping, I take this to heart. I can easily go 10-20 scraping cycles without digging a big hole when scraping individual scrapes.
-- No chicken scratches!
-- I'm forgetting one...
- For this drill press table, I scraped it on the drill press. It pivots, and is height adjustable, so it was a very convenient place to scrape. Normally I would scrape on my bench.

 

[george wilson]

A nice looking job,but have you checked to see if the spindle of the drill press is square to the table? A friend bought an imported drill press(Taiwan made) back in the 80's. I took some instruments to his house,and found that the front edge of the drill press table was grossly too high. I mean about 1/16" !! There was a steel button on the back side of the table where it swiveled. I filed it down so the table was reasonably square to the spindle. You want a FEW thou. high in the front,but not what that table started out to be.

 

[Erik Brewster]

That table looks great, not only is it flat it looks good. I'm assuming you took one of Richards classes? I would love to learn scraping but it might have to be a self taught en-devour.

I took Richard's class in Oakland a couple of years back. I can't say enough good things about it. His DVD is really good, but it's hard to replace an expert looking over your shoulder giving you tips.

I do think scraping is self-teachable, if you are persistent and reflective. Like many skills, spend the time to get some solid fundamentals before you tackle a big project.

- - - Updated - - -

A nice looking job,but have you checked to see if the spindle of the drill press is square to the table? A friend bought an imported drill press(Taiwan made) back in the 80's. I tool some instruments to his house,and found that the front edge of the drill press table was grossly too high. I mean about 1/16" !! There was a steel button on the back side of the table where it swiveled. I filed it down so the table was reasonably square to the spindle. You want a FEW thou. high in the front,but not what that table started out to be.

That's a good point. I'll have to take that on at some point.

 

[Richard King]

Nice job Erik, :goodjob:

I haven't said much because I want everyone to read and see how good "they" can scrape after only 3 days of instruction and 2 or 3 years of practice. I also want to thank Erik as he has been contributing to the forum in several threads. The other articles from Jan,Bill, Mel, Jim and the rest (who did I forget, sorry) are proof that scraping is not that difficult to do as long as you follow a few simple rules. I appreciate what Erik said about standing behind him and showing. I have heard this before from Glen who took the Dallas class a few years ago. He said he had read and re-read the Connelly book and it never clicked until I showed him how. Remember what I say, scraping flatness is easy, but knowing where to scrape and how much to take off is the hard part of the trade of Machine Tool Rebuilding. To get the alignment and geometry right. Practice makes perfect.

That is another reason I love this web-site and the vision or gift from God that Nelson received when he created it. Hobby-Machinist encourages you to show your work and teach. There are some real Craftsmen here. I hope everyone has seen the "art" George Wilson makes. He is truly an Artist and Craftsman.

It's like anything else as if you have following TomG and his You Tube DVD's (not sure the exact word on what they call those) but he is a great teacher and it's so simple when you have a guy behind you showing you how compared to trial and error learning. As I have said before I was lucky and learned from my Dad and with his help and advice when I was a little kid have been able to pass on his knowledge. I want my students to pass on what I have shown you. I encourage you students and none students to not be shy and show us your work here or at your work. I am so proud that Bill from the GA class wrote and told me he has been teaching some machine shop classes and including scraping down in Georgia at a Technical colledge. I want to stand back and let you teach, not say much, let you have the glory, so to speak. I am sorry if those words to some think come off in your minds as if I am bragging. I can't always be as elegant as some writers are and have tried and tried to say it in a different way, but this is how I say it.

The checkerboard, depth of the scraping and mapping (as I say being a detective and have a game plan) the part Erik has showed you is the key to a good scrape job. It's amazing how pushing on a hand tool can be better then the most sophisticated machines built today can machine. Engineers have long tried to find ways to eliminate scraping, but can't.

Thanks Erik for sharing your Art and hard work. :thumbsup: Rich

 

[Erik Brewster]

A few notes:
- The hole in the paper is 1" x 1". I don't have the Biax gauge, so a cheap paper gauge it is I should have written the dimensions on it...
- I have a little chatter on the t bolt slots that you can't see. It isn't bad though -- it will still blue up, just a bit ugly when looking close. For me, the trick to keeping it under control is to approach it from a good angle. If you start perpendicular from a ledge and scrape away from it, you will gouge it badly. When I wanted to scrape perpendicular to a ledge, I would start a distance away from it. When I was done with that section, I would turn the part 180 degrees and scrape towards the ledge, not starting at it. The scraper running off the ledge is not so bad...
- The picture of the blue mark with the paper is 10-20% contact. It's probably one of the worst places and there are a lot of 50% areas that are better. If this was a sliding way or other critical area, I would have more work to do. This was a "quick" job on a cheap drill press and I stopped as soon as it was flat with no big "holes" where the blue did not show up. I think this quality is not acceptable on a lathe or mill way or anything of similar quality.
- I didn't talk about it much, but attacking the roughing like you are reading a topographical map is important. It's good to do one overall scrape to get through the surface and get everything scraped. After that, stick to the topographical map technique. It's SOOOO easy to start digging a hole in the name of being "smart" and trying to do something smarter than the topographical map method. I didn't measure the table. I suppose I should have. I could have drawn a proper topographical map every 0.001" or so and I could have scraped 10 or more cycles before blueing the table. I didn't, so I would (during roughing) blue the table and scrape twice (90 degrees opposed) and repeat until I hit the finishing stage. I might have saved an hour out of five if I had done that.

 

[jshaugjord]

Hello Erik,

I understad what you mean, but I don't think it looks ugly at all! Rather the opposite.. Scraping finish has a pleasant look.
I also know what you are saying about the topography, and using this as a guide.

It sure takes time, doesn't it.. this must be answering to the term "labor intensive work"

PS! I am still amazed also what can be learnt from the "hinge test". One almost seems to be able to blind scrape using only this as a guide.

Keep up the good work. I may be biased (machine addict or a few other names), but I really enjoy watching the progression of such a project and all that comes with

Jan