Tips for Accurate Measuring and Machining

[Monitrech]

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]

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]

Originally Posted by wilful

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]

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]

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]

Originally Posted by Pat Fairbank

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]

Originally Posted by RoboChair

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]

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!

[FrankJ]

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.

[Charles Boehm]

Originally Posted by Pat Fairbank

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.

[DonRotolo]

Originally Posted by Pat Fairbank

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.

Requoted for truth.
If you use a sharpie with a 1/8" thick tip to mark your spot, the best accuracy you'll get is 1/8". Instead, use the marker to mark nearly the spot, then use a scribe or other sharp object to mark exactly the spot.

If you make a cross or X with a scribe, you can 'feel' the intersection of the lines with your center punch, ensuring you hit the mark perfectly.

Measurement and markout is a skill and the techniques can be learned, just put in some effort and don't settle for 'close enough'. After a while you'll get fast at it too.

[GeeTwo]

A neat trick that works for some applications is to use perforated breadboard to line things up. The holes are already present at 0.1" apart, so if you can work out your spacings on that grid and fit pieces within a relatively small area, it's great. Just mark which holes to drill, and line up on these as pilots. If you're going to do multiple copies of a piece, use a 1/16" bit as a pilot for your stock, then follow up with the actual size hole. This trick is especially useful for making "control panels" and similar applications where you want everything to line up evenly, but exactly WHAT the spacing is isn't critical. OBTW, use the stuff WITHOUT solder pads for this!

[dradel]

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

[Cyberphil]

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).

[Monitrech]

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