Expectations / Capabilities / Accuracy of mini-mills/lathes

[theoldwizard1]

Total newbie, so I ask silly questions, or don't really ask the correct question.

First, I understand from the discussion that we had on calipers this measuring tool "gets you in the ball park". If you really want to measure a part accurately you will need a micrometer or a dial gauge or other appropriate high accuracy instrument.

When I buy my mill, I will probably be making things like mounts/brackets for marine/automotive application, mostly out of aluminum, but plastic or mild steel are not out of the question.

One item I recently purchased was made out of 3 - 1/2" aluminum plates, joined at the edge with 1/4" flat head screws to form a C-channel (it was made this way because there was machining on the inside faces). A very shallow rabbet was cut on the side pieces to help align the back, but you were still drilling a #7 hole into the edge of a 1/2" aluminum plate that had to line up with a 1/4" countersunk hole on the side plate. Locating the hole off of the edges of 2 different work pieces is obviously important.

So how close is "close enough" for hole location on a job like this ? +/-0.002, +/-0.005, +/-0.010 ? Is a a min-mill capable of doing this (assuming the operator knows how to correctly find the edges and crank in the location).


The wood worker in me would just clamp the pieces together and drill the pilot hole for the screw through the side of one piece into the edge of the other. Of course we are talking 1" nominal boards.

 

[zmotorsports]

Some of that will depend on the diameter of the holes in relation to the fasteners. If you holes will allow some movement of the plates then you can be off a bit and still be able to fasten them together. Personally, that is not the way I like to do things.

Tasks you will need to be proficient at will be finding the center of a hole and accurately drilling and tapping said hole. Also you must be able to accurately pick up an edge with a center and then drill at the proper measurement for the fastener.

These are things that may sound tedious or difficult at first, however, for an experiencer person picking up and edge with an edge finder and moving X distance is actually quite easy. Practice and get to know your machine as these will help to develop those skills.

As far as a small milling machine or a mill/drill being capable, the answer would be yes. That said, much of that will be not only in the skill level of the person running the machine but also in how you set up your work to perform the tasks and especially how rigid you set up the work. You will not be able to hold tight tolerances if the work moves at all when the machining process begins.

Mike.

 

[JimDawson]

+ 1 what Mike said. In addition to that, when I have to drill & tap a series of holes to hold two parts together, I will drill & tap the first hole, taping through both pieces then screw a bolt in to hold the alignment. Then do the same with the next couple of holes. That way even if you are a bit off everything still fits. Then dissemble the parts, and go back and clearance drill and C-sink the holes. Once you have the holes started, you could do the last operation in a drill press or many times with a hand drill because is normally not necessary to fixture the part to get the holes correct.

 

[darkzero]

Generally speaking in relation to the thread title, mini machines are very capable & that includes the less expensive ones from say like HF. My first lathe was a HF 8x14 mini & if it wasn't for that I would have never found my love for machining. With just a few upgrades & modifications it was a great lathe, only problem was that I out grew it in less than 8 months.

Some may not be as great out the box, simlple minor upgrades like quality fastners in certain areas can drastically change the accuracy & quality of use of the machine. Only downsides to a small machine is capacity but that doesn't always stop a lot of mini owners. I give mini owners a lot of credit, some of the most ingenious mods & attachments come from mini owners who find great ways of overcoming limitations & work capacities.

 

[Rbeckett]

Mini Mills and Lathes are great little machines to get into our hobby. If it weren't for them I would never have become involved in such a fun and interesting past time The smaller machines are actually quite capable of achieving sub .001 accuracy if you take the time to set the operation up properly and find all of the benchmarks accurately. Practice will make perfect really applies to our hobby and the smaller mills and lathes can and do achieve this on a regular basis. Some of the lower priced offerings di need some TLC and basic adjustments straight out of the box, but with a few minor modifications and a little attention to detail they do come around quite nicely. I would tend to avoid the cheapest possible machines because the quality control does tend to be spotty, but I did get lucky when I got my two HF machines. If you are interested in a little better quality machine I would suggest a Precision Mathews and possibly a Grizzly. PM seems to be a very high quality machine for the money and I have only heard ONE complaint about the machine in all the time I have been involved in this hobby (10 years). So welcome to the club and don't hesitate to jump in and learn along with the rest of us!!!

Bob