What is the limit?
“The maximum discount allowed in a basic size at which parts can be made is called the limit of that size”.
When parts are produced in a workshop, the worker is allowed to make the basic sizes of the parts slightly larger or smaller. This exemption is given so much that it does not affect the part. Because there are many reasons like this. Due to which the part cannot be made in exactly the exact size. For example, fault of micrometer tools, fault of machine setting, fault of tool etc. Due to this, there may be some difference in size while making the parts. Apart from this, even if the parts are made to the correct precision measurement, then the time is more, so the limit is set for making the part. That the part can be made in more or less size than the basic size, this makes it easy for the artisan to make the size of the part. And the parts made in this limit do not get spoiled. If the basic size of the shaft is 50 mm, and there is a relaxation of – 0.02 mm to +0.02 mm, then this shaft with 50 mm basic size will be divided into (50-0.02) 49.98 mm to (50+0.02) 50.02 mm. Can be made in any size inside.
Upper Limit=50+0.02=50.02 mm
Lower Limit=50-0.02=49.98 mm
More Information:- Hacksaw Blade About teeth setting
To reveal the maximum size of the job, the allowed relaxation in its original size is called its upper limit; For example, if basic size = 50 mm, discount = +0.02 mm, -0.02 mm
So its upper limit is +0.02 mm
And upper limit size = 50.02 mm.
To reveal the minimum size of the job, the relaxation allowed in its original size is called its lower limit;
For example, the lower limit of the job = -0.02 mm
And lower limit size=50.00-0.02=49.98 mm.
Here, by the Basic Size, we mean the size on which the limitation has been done by giving exemption; For example- 50 +0.02mm, the basic size is 50mm in the dimension of -0.02mm.
By actual size, we mean the size of the job which is actually obtained by measuring it after machining. If the actual size is less than the lower limit size More And if the upper limit is less than the size then the job is passed (OK) but if the actual size is less than the lower limit or more than the upper limit then the job is rejected.
There are several systems for determining job limits and fits; like-
- International Standard Organization (ISO)
- British Standard System (BSS)
- Bureau of Indian Standard (BIS)
- Newale System
In our country (India) the work is done on the rules set by BIS. Under this, the part of the inner size (in which another part fits) in the parts that fit together is called the hole and the part with the outer size is called the shaft.
More Information:- About setting the teeth of the hacksaw blade