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Monitrech 22-12-2014 00:05

Tips for Accurate Measuring and Machining
 
We do most of our machining by hand using only tape measures and calipers for measurements and sometimes have a difficult time properly marking and cutting or drilling accurately. I was wondering if anybody had any recommendations for tricks and best practices to get more accurate cuts (and hole placement in particular).

wilful 22-12-2014 00:15

Re: Tips for Accurate Measuring and Machining
 
If you use cad, you can print out 1:1 drawings and glue the to the part. might not look the prettiest afterwards, but it works.

Mr V 22-12-2014 00:31

Re: Tips for Accurate Measuring and Machining
 
Quote:

Originally Posted by wilful (Post 1415795)
If you use cad, you can print out 1:1 drawings and glue the to the part. might not look the prettiest afterwards, but it works.

Just use a small amount of rubber cement to attach the paper to the part and then you can remove it and rub the residue off.

asid61 22-12-2014 00:32

Re: Tips for Accurate Measuring and Machining
 
What resources do you have? That will factor a lot in what you are doing.
To get really accurate placement of holes and edges, you should buy a height gauge on ebay. Only around $40 for a 12" tall one. Then buy a large steel plate or even better a granite surface plate. Use the two in conjunction to mark out lines and coordinates accurate to 0.001".
Invest in an angle plate, 1-2-3 blocks, or even just a good square to orient parts correctly.
We use a 36" ruler graduated in increments of .01" to mark out locations for long parts like WCD side rails. A loupe/ magnifying glass makes the small graduations easier to read.

If you can't afford the above, just get a 12" ruler graduated in increments of 0.01". Use that and a scribe to mark out coordinates for holes.

If you need holes to line up on 2x1, mmark one side and drill through with a small drill. Then drill both sides, one at a time or together, with the larger drill.

Use a punch to get hole locations accurate after you have coordinates marked out.

Pat Fairbank 22-12-2014 00:58

Re: Tips for Accurate Measuring and Machining
 
Like Anand said, you can get pretty good precision with hand measuring tools. A surprising number of parts/features on our robots (brackets, angled cuts, etc.) are made this way.

My favorite set of low-tech tools for laying out holes and lines consists of a combination square, a blue marker, a scribe, and a center punch. When marking a hole, for instance, you can set the combination square to the X and Y distances to the hole from the edges of the workpiece, and scribe two lines to establish the point (use the blue marker to provide some contrast before scribing). Then mark the hole with a center punch, and drill with a center drill before the actual size you want, as twist drills tend to walk.

RoboChair 22-12-2014 02:12

Re: Tips for Accurate Measuring and Machining
 
Quote:

Originally Posted by Pat Fairbank (Post 1415801)
Like Anand said, you can get pretty good precision with hand measuring tools. A surprising number of parts/features on our robots (brackets, angled cuts, etc.) are made this way.

My favorite set of low-tech tools for laying out holes and lines consists of a combination square, a blue marker, a scribe, and a center punch. When marking a hole, for instance, you can set the combination square to the X and Y distances to the hole from the edges of the workpiece, and scribe two lines to establish the point (use the blue marker to provide some contrast before scribing). Then mark the hole with a center punch, and drill with a center drill before the actual size you want, as twist drills tend to walk.

Give this man a cookie! This method WORKS!!! And is very easy to do, and calipers can also be used to scribe in lines.

Mike Marandola 22-12-2014 02:22

Re: Tips for Accurate Measuring and Machining
 
Quote:

Originally Posted by RoboChair (Post 1415804)
Give this man a cookie! This method WORKS!!! And is very easy to do, and calipers can also be used to scribe in lines.

While a fast method, it's not very good practice unless you have scribing calipers which have carbide tips. If you are going to do it, use a cheap pair, make sure your students know not to scribe with the $100 pair, and only on soft materials.

3476 has some great layout tutorials using a pair of calipers and a scribe on their website.

IronBenderII 22-12-2014 12:13

Re: Tips for Accurate Measuring and Machining
 
We have struggled with the same thing so this year we invested in Incra Rules/scribes/Dykem Blue this year and so far it's helped a ton.

http://smile.amazon.com/s/ref=nb_sb_...le%2Caps%2C325

http://smile.amazon.com/gp/product/B...?ie=UTF8&psc=1

Hope this helps!

dradel 22-12-2014 12:39

These are great for marking holes
http://www.atgstores.com/chisels-pun...g&gclsrc=aw.ds

FrankJ 22-12-2014 12:47

Re: Tips for Accurate Measuring and Machining
 
I would avoid using calipers as a scribe. Inexperienced eyes are watching & may not not understand when not to do it.

Beware of the thickness line that the tool you use to mark. You can make a V with the apex of the V being center of the mark. Be aware of the offset of the scribe to the straight edge.

Cyberphil 22-12-2014 13:59

Re: Tips for Accurate Measuring and Machining
 
One tip I picked up from working at a machine shop is make a quick vice end stop if you are making many identical holes or features on parts. You can make them or buy them for most vice types, and they can make your life much easier.

This device is also amazing if you decide to take the part off to test it and must re-install it on the vice for further machining (for prototyping and the like).

Another must-have tool for machinists is an edge finder. They are very cheap and can be quite accurate and precise. As long as you have a smooth surface to use it on you can get very tight zero locations on your CNC machines. I used a regular $15 edge finder at a reference standard company that required location tolerances of 0.0001-0.00005" and with some practice the edge finder was able to get those tolerances (not that you will need anything near that in FRC).

Charles Boehm 22-12-2014 14:08

Re: Tips for Accurate Measuring and Machining
 
Quote:

Originally Posted by Pat Fairbank (Post 1415801)
Like Anand said, you can get pretty good precision with hand measuring tools. A surprising number of parts/features on our robots (brackets, angled cuts, etc.) are made this way.

My favorite set of low-tech tools for laying out holes and lines consists of a combination square, a blue marker, a scribe, and a center punch. When marking a hole, for instance, you can set the combination square to the X and Y distances to the hole from the edges of the workpiece, and scribe two lines to establish the point (use the blue marker to provide some contrast before scribing). Then mark the hole with a center punch, and drill with a center drill before the actual size you want, as twist drills tend to walk.

Our team uses this for most everything we cut that isnt on the vertical mill or the lathe.

Monitrech 22-12-2014 14:52

Re: Tips for Accurate Measuring and Machining
 
I found this pdf explaining how to use caliper tips as scribes for accurate measuring, although it doesn't look too good for the calipers.

http://www.botlanta.org/uploads/pdf/caliper_abuse.pdf

themccannman 22-12-2014 16:52

Re: Tips for Accurate Measuring and Machining
 
Buy some cheap calipers that are used for light scribing and hand made parts. Keep the expensive calipers/micrometers with the machines where they are used specifically for measuring part tolerances. Also, most of us are using 6061 aluminum, it will take a while to damage the tip of a steel caliper as long as you aren't trying to cut your part using the ends. When you use marker to pre-mark the surface before etching you barely even have to touch the surface to make your line.

AmiableVariable 22-12-2014 17:38

Re: Tips for Accurate Measuring and Machining
 
As mentioned above, for a lot of layout, a good square, a sharp pencil, fine tip sharpie or scribe and layout die, and ruler are your best friends. Height gages are also incredibly helpful, though do make sure that the surface being marked is perpendicular to the surface the height gauge is resting on. Tape measures are usually better for longer pieces. Also, thinner layout lines and marks allow for higher precision.

First off, make sure everyone manufacturing parts remembers to consistently zero calipers and measure from zero on the rulers, not the end.

Regardless of which tools you get: Pick your battles, and be sure you have the best (least variation) possible reference points.

For example, it's less precise to use a rough cut edge (cut with bandsaw or hacksaw) as a reference point to mark out holes, because it gives an uneven starting point. It would be better to mark a straight line that is perpendicular to a trustworthy side (or a set of perpendicular lines, if everything is rough cut) and measure the distances from that. If this is done before the final cut of the shape, you could later use those reference lines to cut the final edges.

When drilling holes to mount parts like a versa-planetary, mark the center for where the shaft is going to go first, because that is typically going to be the most important part relative to the rest of the design. Then, mark up the centers for the rest of the mounting holes relative to the critical center-point, not from the edges of the part. Unless it's a very compact design, having a slight rotation in the motor mount should cause a less trouble than an incorrect distance between mounting holes. If the rotational alignment is important, pick the two most important points on the piece (or the two that are the furthest apart) and measure those first.

When actually drilling hole, center punches and pilot drills help. In regards to cutting pieces, the thinner a line you can give machinists to follow, the better. Additionally, mark which side of the line you would rather have them err on. If you need a smoother line right at the mark, cutting a little large and filing the part down to the line is always an option.

Hope this helps!


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