The bolts are large. I estimate about 5/8" based on the hex diameter. I doubt my one finger push can deflect those ? Dunno. What i was asking, is this typical for these machines ? I dont want to muck with the bolts etc at all. I chose this mill based on the reputation of Precision Matthews quality. I dont need another project, I already have several, this machine was supposed to help me get them done......
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Bench type mill rigidity
- Thread starter gjestico
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I have owned several square column bench top mills and I upgraded from the original Rong Fu 45 to a PM-935 baby knee mill about 8 years ago. In my experience, the Rong Fu was more rigid than this baby knee mill. But you have to set up the benchtop mill properly. I have posted a video on how to check your mill here, but let's deal with the rigidity issue first.
I doubt very seriously that the quality bolts on your 833 are contributing to a lack of rigidity. Yes, if they were not tightened properly, the column could rock, but the comments about "grade 8 bolts" improving rigidity sound like confirmation bias to me. And 0.001" of flex of the column on this mill is certainly within reason if you're pushing on the top of the column with something like 30-40 pounds of force. If you want to see what happens on a PM-935 knee mill, I have a video that illustrates that here.
We could argue how much flex the 833 column should exhibit, but some flex is normal. I would check that you have the head locked down with the Kipp levers when you do the test. You might even want to break the column-to-base connection and set up the tram properly first using instructions such as these. before doing anything, I would also indicate from the XY table directly to the dovetail ways on the column and see what that tells you when you push on the top of the column in both the X and Y directions.
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If that column was 4" E.M.T. it wouldn't flex. Go with DAT510's reply and start using the mill.
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I disagree with David- Chinese bolts are often notoriously soft and rubbery, and they sometimes have internal inclusions and fracture easily. Since my advice was to separate the pieces and clean/inspect, why not upgrade the fasteners? It may not make any measurable improvement but it is an improvement
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Just remember that the standard for comparison of the rigidity of any bench mill is not the Bridgeport. In my opinion, for what little it may be worth, it is normal for all bench type mills to have some rigidity issues. Just like most machinery, the more mass, generally speaking, the greater rigidity.
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My son came over today and hoisted and clamped the cement block to the top of my mill column. It works great, huge difference in sound and vibration. I milled a .200" deep x 3/8" wide slot in aluminum at my normal feed rate and it was smooth as glass. Then I did a .300" deep x 3/8" wide slot at a substantially higher feed rate than I would normally use and again it was smooth and quiet. This was a great side benefit of building the worm drive gearbox as it cleared off the top of my mill column making installation of this weight possible. I'm a happy camper.
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Soft? Yes, that can be true. Rubbery? Steel - no matter what quality - is not rubbery. The column bolts either fail to hold the column rigidly (due to stripped threads), or they perform until they fail. They are not going to "spring back" like a shaft of rubber if they fail. Also, this machine is from Taiwan, not mainland China - my experience suggests the quality of the fasteners from Taiwan are uniformly good quality.
A bolt is in essence a spring to a certain extent. Any one who has any knowledge of torque to yield head bolt vs ARP head studs would understand what I mean by that. Not to say you are wrong about this particular situation. I am speaking from experience on my own mill when I suggested looking into where the bed meets the column. That is precisely where I found my issue. Was simply agreeing with the other fellow who beat me to it. Just trying to help the gentleman find the source of his issues
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I too am trying to help the OP by not sending him off on a wild goose chase. If he decides to adjust the column of the mill as part of tramming it in at the base-to-column connection, it might make sense to upgrade the bolts. I've trammed over a dozen Asian benchtop mills by adjusting the column to base connection and not once have I seen bolts stretch and then return to original condition. I HAVE certainly stripped them, but if that's what's going on here, the column would not spring back to the same position consistently. I'll shut up now and just follow what happens. No reply expected or necessary.
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Is this the mill you are referring to?
Looks like a good quality, light weight hobby bench mill. Every platform has limitations.
My mill is heavy and huge but the work window is satisfying. I have considered downsizing to a PM833TV but I question rigidity and the height from spindle to table is small.
www.precisionmatthews.com
Looks like a good quality, light weight hobby bench mill. Every platform has limitations.
My mill is heavy and huge but the work window is satisfying. I have considered downsizing to a PM833TV but I question rigidity and the height from spindle to table is small.
PM-833TV Ultra Precision Milling Machine – Precision Matthews Machinery Co.
www.precisionmatthews.com