What angle tolerances can machine shops typically hold? 2

[Scott8888]

Hello, we spec an angular tolerance of plus/minus 0.5 degrees on our dwgs, but I know most shops can do better than that. Is plus/minus 0.1 degrees something most shops can hold without breaking a sweat? Thanks for any info, Scott

 

[Screwman1]

On what sized part and what type of feature? That is a pretty broad question. Give us more detail and we will be able to better answer your question. If you are talking about an optical mfg. then they should be able to hold a few seconds without any trouble, if you are talking a welding shop, they may need more than a degree- it depends.

 

[Scott8888]

The parts I design typically have flat features machined out of aluminum 6061-t6 plate, usually around 100mm in size.

 

[mfgenggear]

Scott

yes it can. if the angle is very important. but beware cost will increase.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[MiketheEngineer]

If small pieces - your measuring equipment may come into question - even ambient tempearture can make a difference

 

[mfgenggear]

yes you are correct Mike.
as the precision of the part increases so does the equipment required.
that is why part cost triples.

a grinding or lapping operation may be required depending on the size & requirement.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[ShaggyPE]

There is something similar to this in Machinery Handbook.

http://www.engineeringtoolbox.com/machine-processes-tolerance-grades-d_1367.html

-Dustin
Professional Engineer
Pretty good with SolidWorks

 

[redpicker]

Somehting that should be considered for every dimension you put on a drawing that carries a tolerance: how are you going to have them measure it?

Measuring an angle to within 1/2 degree can usually be done with a machinists protractor. To get better than that, you are probably looking at co-ordinate measuring systems or optical comparators. If you need the added percision, then they will find a way to measure it, but to put a tolerance on a dimension that is tighter than is needed just becasue "they should be able to hold that" is wrong.

If a valve seat needs to be within +/- 5 minutes (for the valve to pass pressure testing, say) then it needs to be specified as such. However, if chamfer can utilize +/- 5 degrees and still work, resorting to +/- 1/2 degree block tolerance just becasue "they should be able to hold that" is not good design practice.

rp

 

[BrianE22]

A milled plate of 100 mm length can easily be produced one side at .1 degrees to the other side on a mill in good condition. That's only about .007"/4". A sine bar is typically used.

 

[mfgenggear]

to inspect angles precisely it must done with the following
sin bar & precision indicators with increments of .0001", .0005" or .001"
optical comparator, the precision depending the system.
CMM

HTH


Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[dgallup]

I find a angular default tolerance of +/-0.5 degrees ludicrous. Default tolerances are for unimportant dimensions where you really don't want to take the time to sit down and calculate the implications of every possible combination of variations because they really are not that important. Like the angle on a chamfer for instance. I think the smallest a default angle tolerance should be it is +/-2 degrees and prefer +/-5 degrees. Then sit down and calculate what you need for any angle that needs to be specified tighter. In many cases you will be better served with a geometric tolerance such as angularity, profile or true position rather than a tight angle tolerance.

----------------------------------------

The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[mfgenggear]

I agree very much so, that verifying angles is a pain.
standard chamfers can be +/- 5 deg & can be held & easily inspected. for medium to small parts ok
in my current world with gears Inside Diameter centers have to be +/- .5 degrees 60 deg included angle.
it is used for tooling. we can hold it all day, we have specialized inspection equipment to verify it.
because this is used for inspecting & grinding, in other cases some special porting requires excessive close angle tolerance.
or for whatever reason. It must have a good rational.

if it's just an edge break or to remove a sharp corner & holds no purpose it is good to clarify
that an excessive close tolerance on a chamfer is not necessary. and should not done.

The way the question was ask by OP is can a angle be held at +/- .5 degree the answer is yes
if it is a very necessary function of the part.

sometime my answers are too brief.

HTH



Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[Cockroach]

Standard tolerance on angles is +/- 1/2 degree. In the old days, manual indexing heads had gearing backlash which contributed to increased dimensional tolerances when diameters became excessivel large.

These days with CNC applications, a guy could specify +/- 1/4 degree without problems.

Regards,
Cockroach

 

[hydtools]

Just because a shop can easily work to tolerances less than you need does not mean you should change your requirement.

Ted

 

[mfgenggear]

Scott

what is the requirement of your part.
is it for required important angles ?


Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[KENAT]

Default tolerances can be problematic. +-.5 degrees is a fairly typical default tolerance. It can be argued that it's a bit tight but given that many folks fail to otherwise specify how perpendicular many edges are etc. keeping it reasonably tight can make sense.

If using any kind of default tolerance then really for every feature/dimension you place you need to think about if the default tolerance is appropriate (primarily function but also manufacturability and inspectability).

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[tbuelna]

Scott8888-

I would agree with the other posters- setting up a machine based on or validating precise angles is a PITA. A better approach is to use linear edge dimensions and/or a system of gauge points. Even CMM's can only validate surface geometry based on the Cartesian coordinates of several measured points.

CNC and CMM machines work off of X,Y,Z values. So forget about using angular dimensions whenever possible.