Screw or weld structure for mounting?

[HMCV]

I am currently designing a semiautomatic machine for a new customer. Regularly, when I have any need for any parts mounted in a structure, I design the structure so that the constituent parts are screwed together. If I require that there is a high precision between the base of the structure and what I mount in it, add dowel pin between the plates that compose them. My client are asking me that these must be welded, instead of screwed.

How can I achievement a high accuracy between the base of the structure and the end plate where I need to mount something, perhaps an actuator or a guide THK?

I have seen many machines where the parts are welded, instead of using screws, and maintain an appropriate reference between the base of the structure and the plate where they will mount an actuator, or guides.
How is this done? I understand that when two parts are welded, these are not linked with adequate precision.
Please refer to the image.

Thank you.

 

[btrueblood]

Use the same alignment techniques as for your screwed parts, i.e. add alignment dowel pin holes. Many times, the alignment features (tabs, slots) can be added to the cut/machined materials and parts for little extra cost. You still need to worry about possible distortion of the base materials due to shrinkage after welding, but this too can be designed around - you might post questions on that subject in the "welding, bonding & fastener engineering" forum.